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 $208.97   10.810%   $231.5597   $231.56   $231.55   $231.60  
  Purchase #2 $121.44   13.338%   $137.6377   $137.64   $137.65   $137.60  
  Purchase #3 $75.53   6.593%   $80.5097   $80.51   $80.50   $80.50  
  Purchase #4 $86.32   9.349%   $94.3901   $94.39   $94.40   $94.40  
  Purchase #5 $238.40   11.551%   $265.9376   $265.94   $265.95   $265.90  
  Purchase #6 $53.92   7.241%   $57.8243   $57.82   $57.80   $57.80  
  Purchase #7 $49.50   10.658%   $54.7757   $54.78   $54.80   $54.80  
  7 purchase totals = $834.08       $922.6348   $922.64   $922.65   $922.60