Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $177.96   10.687%   $196.9786   $196.98   $197.00   $197.00  
  Purchase #2 $194.42   9.416%   $212.7266   $212.73   $212.75   $212.70  
  Purchase #3 $220.95   10.556%   $244.2735   $244.27   $244.25   $244.30  
  Purchase #4 $152.80   11.668%   $170.6287   $170.63   $170.65   $170.60  
  Purchase #5 $241.48   10.847%   $267.6733   $267.67   $267.65   $267.70  
  Purchase #6 $126.40   6.500%   $134.616   $134.62   $134.60   $134.60  
  Purchase #7 $159.59   4.791%   $167.236   $167.24   $167.25   $167.20  
  7 purchase totals = $1,273.60       $1,394.1327   $1,394.14   $1,394.15   $1,394.10