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 $229.74   10.392%   $253.6146   $253.61   $253.60   $253.60  
  Purchase #2 $110.41   10.200%   $121.6718   $121.67   $121.65   $121.70  
  Purchase #3 $60.43   4.220%   $62.9801   $62.98   $63.00   $63.00  
  Purchase #4 $243.97   7.386%   $261.9896   $261.99   $262.00   $262.00  
  Purchase #5 $57.51   12.624%   $64.7701   $64.77   $64.75   $64.80  
  Purchase #6 $224.44   8.122%   $242.669   $242.67   $242.65   $242.70  
  Purchase #7 $63.89   4.842%   $66.9836   $66.98   $67.00   $67.00  
  7 purchase totals = $990.39       $1,074.6788   $1,074.67   $1,074.65   $1,074.80