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 $43.63   11.764%   $48.7626   $48.76   $48.75   $48.80  
  Purchase #2 $89.65   3.607%   $92.8837   $92.88   $92.90   $92.90  
  Purchase #3 $237.66   7.169%   $254.6978   $254.70   $254.70   $254.70  
  Purchase #4 $45.88   9.691%   $50.3262   $50.33   $50.35   $50.30  
  Purchase #5 $236.44   10.865%   $262.1292   $262.13   $262.15   $262.10  
  Purchase #6 $159.40   6.227%   $169.3258   $169.33   $169.35   $169.30  
  Purchase #7 $174.76   5.481%   $184.3386   $184.34   $184.35   $184.30  
  7 purchase totals = $987.42       $1,062.4639   $1,062.47   $1,062.55   $1,062.40