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 $84.62   8.248%   $91.5995   $91.60   $91.60   $91.60  
  Purchase #2 $47.31   13.358%   $53.6297   $53.63   $53.65   $53.60  
  Purchase #3 $86.84   5.699%   $91.789   $91.79   $91.80   $91.80  
  Purchase #4 $220.29   7.290%   $236.3491   $236.35   $236.35   $236.30  
  Purchase #5 $246.98   6.283%   $262.4978   $262.50   $262.50   $262.50  
  Purchase #6 $157.86   10.359%   $174.2127   $174.21   $174.20   $174.20  
  Purchase #7 $116.51   4.185%   $121.3859   $121.39   $121.40   $121.40  
  7 purchase totals = $960.41       $1,031.4637   $1,031.47   $1,031.50   $1,031.40