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 $29.29   13.217%   $33.1613   $33.16   $33.15   $33.20  
  Purchase #2 $211.39   13.133%   $239.1518   $239.15   $239.15   $239.20  
  Purchase #3 $53.62   10.317%   $59.152   $59.15   $59.15   $59.20  
  Purchase #4 $171.54   8.442%   $186.0214   $186.02   $186.00   $186.00  
  Purchase #5 $75.98   10.361%   $83.8523   $83.85   $83.85   $83.90  
  Purchase #6 $129.75   8.401%   $140.6503   $140.65   $140.65   $140.70  
  Purchase #7 $218.39   10.736%   $241.8364   $241.84   $241.85   $241.80  
  7 purchase totals = $889.96       $983.8255   $983.82   $983.80   $984.00