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 $41.73   6.110%   $44.2797   $44.28   $44.30   $44.30  
  Purchase #2 $149.46   12.857%   $168.6761   $168.68   $168.70   $168.70  
  Purchase #3 $81.96   12.268%   $92.0149   $92.01   $92.00   $92.00  
  Purchase #4 $205.68   4.489%   $214.913   $214.91   $214.90   $214.90  
  Purchase #5 $161.30   9.414%   $176.4848   $176.48   $176.50   $176.50  
  Purchase #6 $153.27   11.428%   $170.7857   $170.79   $170.80   $170.80  
  Purchase #7 $83.80   4.344%   $87.4403   $87.44   $87.45   $87.40  
  7 purchase totals = $877.20       $954.5945   $954.59   $954.65   $954.60