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 $16.94   12.247%   $19.0146   $19.01   $19.00   $19.00  
  Purchase #2 $218.57   3.262%   $225.6998   $225.70   $225.70   $225.70  
  Purchase #3 $21.76   9.119%   $23.7443   $23.74   $23.75   $23.70  
  Purchase #4 $62.41   8.258%   $67.5638   $67.56   $67.55   $67.60  
  Purchase #5 $57.72   12.603%   $64.9945   $64.99   $65.00   $65.00  
  Purchase #6 $100.87   8.806%   $109.7526   $109.75   $109.75   $109.80  
  Purchase #7 $228.45   8.745%   $248.428   $248.43   $248.45   $248.40  
  7 purchase totals = $706.72       $759.1976   $759.18   $759.20   $759.20