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 $236.89   10.457%   $261.6616   $261.66   $261.65   $261.70  
  Purchase #2 $169.89   8.844%   $184.9151   $184.92   $184.90   $184.90  
  Purchase #3 $152.70   9.440%   $167.1149   $167.11   $167.10   $167.10  
  Purchase #4 $123.85   9.420%   $135.5167   $135.52   $135.50   $135.50  
  Purchase #5 $118.34   12.362%   $132.9692   $132.97   $132.95   $133.00  
  Purchase #6 $249.67   5.869%   $264.3231   $264.32   $264.30   $264.30  
  Purchase #7 $23.37   7.231%   $25.0599   $25.06   $25.05   $25.10  
  7 purchase totals = $1,074.71       $1,171.5605   $1,171.56   $1,171.45   $1,171.60