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 $215.56   7.583%   $231.9059   $231.91   $231.90   $231.90  
  Purchase #2 $92.61   3.756%   $96.0884   $96.09   $96.10   $96.10  
  Purchase #3 $40.29   3.547%   $41.7191   $41.72   $41.70   $41.70  
  Purchase #4 $92.88   10.149%   $102.3064   $102.31   $102.30   $102.30  
  Purchase #5 $205.34   3.819%   $213.1819   $213.18   $213.20   $213.20  
  Purchase #6 $129.71   6.353%   $137.9505   $137.95   $137.95   $138.00  
  Purchase #7 $189.85   11.688%   $212.0397   $212.04   $212.05   $212.00  
  7 purchase totals = $966.24       $1,035.1919   $1,035.20   $1,035.20   $1,035.20