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 $60.42   3.242%   $62.3788   $62.38   $62.40   $62.40  
  Purchase #2 $246.90   12.171%   $276.9502   $276.95   $276.95   $277.00  
  Purchase #3 $35.98   8.816%   $39.152   $39.15   $39.15   $39.20  
  Purchase #4 $90.50   5.325%   $95.3191   $95.32   $95.30   $95.30  
  Purchase #5 $94.40   11.201%   $104.9737   $104.97   $104.95   $105.00  
  Purchase #6 $224.85   10.119%   $247.6026   $247.60   $247.60   $247.60  
  Purchase #7 $128.27   13.276%   $145.2991   $145.30   $145.30   $145.30  
  7 purchase totals = $881.32       $971.6755   $971.67   $971.65   $971.80