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 $167.61   10.852%   $185.799   $185.80   $185.80   $185.80  
  Purchase #2 $37.57   9.183%   $41.0201   $41.02   $41.00   $41.00  
  Purchase #3 $20.36   13.177%   $23.0428   $23.04   $23.05   $23.00  
  Purchase #4 $209.87   11.654%   $234.3282   $234.33   $234.35   $234.30  
  Purchase #5 $77.56   4.245%   $80.8524   $80.85   $80.85   $80.90  
  Purchase #6 $234.78   13.811%   $267.2055   $267.21   $267.20   $267.20  
  Purchase #7 $144.25   3.134%   $148.7708   $148.77   $148.75   $148.80  
  7 purchase totals = $892.00       $981.0188   $981.02   $981.00   $981.00