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 $89.98   5.187%   $94.6473   $94.65   $94.65   $94.60  
  Purchase #2 $87.97   4.526%   $91.9515   $91.95   $91.95   $92.00  
  Purchase #3 $155.79   12.415%   $175.1313   $175.13   $175.15   $175.10  
  Purchase #4 $126.83   7.607%   $136.478   $136.48   $136.50   $136.50  
  Purchase #5 $82.96   3.666%   $86.0013   $86.00   $86.00   $86.00  
  Purchase #6 $113.92   8.145%   $123.1988   $123.20   $123.20   $123.20  
  Purchase #7 $110.40   13.656%   $125.4762   $125.48   $125.50   $125.50  
  7 purchase totals = $767.85       $832.8844   $832.89   $832.95   $832.90