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 $210.86   6.667%   $224.918   $224.92   $224.90   $224.90  
  Purchase #2 $22.92   10.131%   $25.242   $25.24   $25.25   $25.20  
  Purchase #3 $223.49   12.663%   $251.7905   $251.79   $251.80   $251.80  
  Purchase #4 $166.42   4.464%   $173.849   $173.85   $173.85   $173.80  
  Purchase #5 $169.94   8.156%   $183.8003   $183.80   $183.80   $183.80  
  Purchase #6 $141.35   4.753%   $148.0684   $148.07   $148.05   $148.10  
  Purchase #7 $60.74   6.429%   $64.645   $64.65   $64.65   $64.60  
  7 purchase totals = $995.72       $1,072.3132   $1,072.32   $1,072.30   $1,072.20