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 $201.38   4.699%   $210.8428   $210.84   $210.85   $210.80  
  Purchase #2 $73.69   13.127%   $83.3633   $83.36   $83.35   $83.40  
  Purchase #3 $165.44   8.402%   $179.3403   $179.34   $179.35   $179.30  
  Purchase #4 $59.70   13.521%   $67.772   $67.77   $67.75   $67.80  
  Purchase #5 $97.29   10.840%   $107.8362   $107.84   $107.85   $107.80  
  Purchase #6 $177.79   13.494%   $201.781   $201.78   $201.80   $201.80  
  Purchase #7 $169.81   5.570%   $179.2684   $179.27   $179.25   $179.30  
  7 purchase totals = $945.10       $1,030.2040   $1,030.20   $1,030.20   $1,030.20