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 $165.90   10.287%   $182.9661   $182.97   $182.95   $183.00  
  Purchase #2 $110.61   13.332%   $125.3565   $125.36   $125.35   $125.40  
  Purchase #3 $191.72   5.852%   $202.9395   $202.94   $202.95   $202.90  
  Purchase #4 $59.57   7.117%   $63.8096   $63.81   $63.80   $63.80  
  Purchase #5 $165.45   12.310%   $185.8169   $185.82   $185.80   $185.80  
  Purchase #6 $108.42   8.443%   $117.5739   $117.57   $117.55   $117.60  
  Purchase #7 $66.82   4.148%   $69.5917   $69.59   $69.60   $69.60  
  7 purchase totals = $868.49       $948.0542   $948.06   $948.00   $948.10