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 $50.66   7.737%   $54.5796   $54.58   $54.60   $54.60  
  Purchase #2 $229.95   4.833%   $241.0635   $241.06   $241.05   $241.10  
  Purchase #3 $165.87   9.735%   $182.0174   $182.02   $182.00   $182.00  
  Purchase #4 $205.40   4.758%   $215.1729   $215.17   $215.15   $215.20  
  Purchase #5 $101.79   7.257%   $109.1769   $109.18   $109.20   $109.20  
  Purchase #6 $98.43   12.232%   $110.47   $110.47   $110.45   $110.50  
  Purchase #7 $178.75   12.170%   $200.5039   $200.50   $200.50   $200.50  
  7 purchase totals = $1,030.85       $1,112.9842   $1,112.98   $1,112.95   $1,113.10