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 $173.54   5.786%   $183.581   $183.58   $183.60   $183.60  
  Purchase #2 $208.91   13.288%   $236.67   $236.67   $236.65   $236.70  
  Purchase #3 $27.33   13.181%   $30.9324   $30.93   $30.95   $30.90  
  Purchase #4 $181.55   11.697%   $202.7859   $202.79   $202.80   $202.80  
  Purchase #5 $101.25   9.633%   $111.0034   $111.00   $111.00   $111.00  
  Purchase #6 $39.80   11.408%   $44.3404   $44.34   $44.35   $44.30  
  Purchase #7 $125.35   6.511%   $133.5115   $133.51   $133.50   $133.50  
  7 purchase totals = $857.73       $942.8246   $942.82   $942.85   $942.80