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 $179.61   13.165%   $203.2557   $203.26   $203.25   $203.30  
  Purchase #2 $207.30   10.688%   $229.4562   $229.46   $229.45   $229.50  
  Purchase #3 $216.52   8.842%   $235.6647   $235.66   $235.65   $235.70  
  Purchase #4 $70.27   4.746%   $73.605   $73.61   $73.60   $73.60  
  Purchase #5 $97.47   10.846%   $108.0416   $108.04   $108.05   $108.00  
  Purchase #6 $89.89   3.620%   $93.144   $93.14   $93.15   $93.10  
  Purchase #7 $97.69   7.271%   $104.793   $104.79   $104.80   $104.80  
  7 purchase totals = $958.75       $1,047.9602   $1,047.96   $1,047.95   $1,048.00