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 $183.83   10.247%   $202.6671   $202.67   $202.65   $202.70  
  Purchase #2 $96.90   3.145%   $99.9475   $99.95   $99.95   $99.90  
  Purchase #3 $33.34   7.776%   $35.9325   $35.93   $35.95   $35.90  
  Purchase #4 $141.62   7.681%   $152.4978   $152.50   $152.50   $152.50  
  Purchase #5 $146.56   7.327%   $157.2985   $157.30   $157.30   $157.30  
  Purchase #6 $122.84   10.356%   $135.5613   $135.56   $135.55   $135.60  
  Purchase #7 $10.44   10.129%   $11.4975   $11.50   $11.50   $11.50  
  7 purchase totals = $735.53       $795.4022   $795.41   $795.40   $795.40