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 $246.31   11.218%   $273.9411   $273.94   $273.95   $273.90  
  Purchase #2 $71.74   7.293%   $76.972   $76.97   $76.95   $77.00  
  Purchase #3 $145.39   9.741%   $159.5524   $159.55   $159.55   $159.60  
  Purchase #4 $167.51   10.323%   $184.8021   $184.80   $184.80   $184.80  
  Purchase #5 $229.53   10.470%   $253.5618   $253.56   $253.55   $253.60  
  Purchase #6 $50.91   7.554%   $54.7557   $54.76   $54.75   $54.80  
  Purchase #7 $170.54   8.674%   $185.3326   $185.33   $185.35   $185.30  
  7 purchase totals = $1,081.93       $1,188.9177   $1,188.91   $1,188.90   $1,189.00