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 $234.51   9.562%   $256.9338   $256.93   $256.95   $256.90  
  Purchase #2 $73.72   4.188%   $76.8074   $76.81   $76.80   $76.80  
  Purchase #3 $110.65   13.487%   $125.5734   $125.57   $125.55   $125.60  
  Purchase #4 $193.56   3.573%   $200.4759   $200.48   $200.50   $200.50  
  Purchase #5 $11.93   11.704%   $13.3263   $13.33   $13.35   $13.30  
  Purchase #6 $211.98   9.632%   $232.3979   $232.40   $232.40   $232.40  
  Purchase #7 $194.31   8.467%   $210.7622   $210.76   $210.75   $210.80  
  7 purchase totals = $1,030.66       $1,116.2769   $1,116.28   $1,116.30   $1,116.30