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 $41.68   13.476%   $47.2968   $47.30   $47.30   $47.30  
  Purchase #2 $219.43   6.696%   $234.123   $234.12   $234.10   $234.10  
  Purchase #3 $154.35   10.592%   $170.6988   $170.70   $170.70   $170.70  
  Purchase #4 $108.68   10.154%   $119.7154   $119.72   $119.70   $119.70  
  Purchase #5 $96.79   8.801%   $105.3085   $105.31   $105.30   $105.30  
  Purchase #6 $91.91   13.584%   $104.3951   $104.40   $104.40   $104.40  
  Purchase #7 $231.82   3.592%   $240.147   $240.15   $240.15   $240.10  
  7 purchase totals = $944.66       $1,021.6846   $1,021.70   $1,021.65   $1,021.60