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 $67.68   11.235%   $75.2838   $75.28   $75.30   $75.30  
  Purchase #2 $29.51   12.514%   $33.2029   $33.20   $33.20   $33.20  
  Purchase #3 $197.39   3.494%   $204.2868   $204.29   $204.30   $204.30  
  Purchase #4 $203.45   8.583%   $220.9121   $220.91   $220.90   $220.90  
  Purchase #5 $223.75   11.858%   $250.2823   $250.28   $250.30   $250.30  
  Purchase #6 $144.67   9.220%   $158.0086   $158.01   $158.00   $158.00  
  Purchase #7 $250.60   4.114%   $260.9097   $260.91   $260.90   $260.90  
  7 purchase totals = $1,117.05       $1,202.8862   $1,202.88   $1,202.90   $1,202.90