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 $243.46   7.169%   $260.9136   $260.91   $260.90   $260.90  
  Purchase #2 $157.42   13.521%   $178.7048   $178.70   $178.70   $178.70  
  Purchase #3 $75.32   10.810%   $83.4621   $83.46   $83.45   $83.50  
  Purchase #4 $23.31   12.645%   $26.2575   $26.26   $26.25   $26.30  
  Purchase #5 $35.83   11.185%   $39.8376   $39.84   $39.85   $39.80  
  Purchase #6 $143.95   6.273%   $152.98   $152.98   $153.00   $153.00  
  Purchase #7 $129.29   3.120%   $133.3238   $133.32   $133.30   $133.30  
  7 purchase totals = $808.58       $875.4794   $875.47   $875.45   $875.50