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 $73.38   10.794%   $81.3006   $81.30   $81.30   $81.30  
  Purchase #2 $101.53   12.438%   $114.1583   $114.16   $114.15   $114.20  
  Purchase #3 $147.40   11.114%   $163.782   $163.78   $163.80   $163.80  
  Purchase #4 $33.34   12.767%   $37.5965   $37.60   $37.60   $37.60  
  Purchase #5 $170.33   12.511%   $191.64   $191.64   $191.65   $191.60  
  Purchase #6 $106.93   11.627%   $119.3628   $119.36   $119.35   $119.40  
  Purchase #7 $238.50   12.378%   $268.0215   $268.02   $268.00   $268.00  
  7 purchase totals = $871.41       $975.8617   $975.86   $975.85   $975.90