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 $52.56   4.110%   $54.7202   $54.72   $54.70   $54.70  
  Purchase #2 $90.44   13.708%   $102.8375   $102.84   $102.85   $102.80  
  Purchase #3 $212.57   7.343%   $228.179   $228.18   $228.20   $228.20  
  Purchase #4 $156.33   13.403%   $177.2829   $177.28   $177.30   $177.30  
  Purchase #5 $247.36   5.167%   $260.1411   $260.14   $260.15   $260.10  
  Purchase #6 $169.55   7.552%   $182.3544   $182.35   $182.35   $182.40  
  Purchase #7 $231.31   5.273%   $243.507   $243.51   $243.50   $243.50  
  7 purchase totals = $1,160.12       $1,249.0221   $1,249.02   $1,249.05   $1,249.00