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 $198.26   11.341%   $220.7447   $220.74   $220.75   $220.70  
  Purchase #2 $159.65   13.693%   $181.5109   $181.51   $181.50   $181.50  
  Purchase #3 $170.29   5.189%   $179.1263   $179.13   $179.15   $179.10  
  Purchase #4 $209.84   3.838%   $217.8937   $217.89   $217.90   $217.90  
  Purchase #5 $66.94   3.774%   $69.4663   $69.47   $69.45   $69.50  
  Purchase #6 $149.43   11.311%   $166.332   $166.33   $166.35   $166.30  
  Purchase #7 $123.27   6.234%   $130.9547   $130.95   $130.95   $131.00  
  7 purchase totals = $1,077.68       $1,166.0286   $1,166.02   $1,166.05   $1,166.00