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 $89.83   9.289%   $98.1743   $98.17   $98.15   $98.20  
  Purchase #2 $183.94   7.404%   $197.5589   $197.56   $197.55   $197.60  
  Purchase #3 $226.85   12.712%   $255.6872   $255.69   $255.70   $255.70  
  Purchase #4 $83.78   13.532%   $95.1171   $95.12   $95.10   $95.10  
  Purchase #5 $152.86   3.259%   $157.8417   $157.84   $157.85   $157.80  
  Purchase #6 $19.45   13.778%   $22.1298   $22.13   $22.15   $22.10  
  Purchase #7 $128.96   7.377%   $138.4734   $138.47   $138.45   $138.50  
  7 purchase totals = $885.67       $964.9824   $964.98   $964.95   $965.00