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 $223.61   9.166%   $244.1061   $244.11   $244.10   $244.10  
  Purchase #2 $210.34   12.377%   $236.3738   $236.37   $236.35   $236.40  
  Purchase #3 $226.85   3.807%   $235.4862   $235.49   $235.50   $235.50  
  Purchase #4 $27.91   12.658%   $31.4428   $31.44   $31.45   $31.40  
  Purchase #5 $45.87   12.259%   $51.4932   $51.49   $51.50   $51.50  
  Purchase #6 $31.45   5.473%   $33.1713   $33.17   $33.15   $33.20  
  Purchase #7 $179.67   13.421%   $203.7835   $203.78   $203.80   $203.80  
  7 purchase totals = $945.70       $1,035.8569   $1,035.85   $1,035.85   $1,035.90