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 $188.31   8.332%   $204   $204.00   $204.00   $204.00  
  Purchase #2 $220.90   11.860%   $247.0987   $247.10   $247.10   $247.10  
  Purchase #3 $62.92   5.313%   $66.2629   $66.26   $66.25   $66.30  
  Purchase #4 $23.40   5.489%   $24.6844   $24.68   $24.70   $24.70  
  Purchase #5 $117.63   9.585%   $128.9048   $128.90   $128.90   $128.90  
  Purchase #6 $189.56   5.480%   $199.9479   $199.95   $199.95   $199.90  
  Purchase #7 $152.51   6.849%   $162.9554   $162.96   $162.95   $163.00  
  7 purchase totals = $955.23       $1,033.8541   $1,033.85   $1,033.85   $1,033.90