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 $107.40   9.835%   $117.9628   $117.96   $117.95   $118.00  
  Purchase #2 $210.33   12.409%   $236.4298   $236.43   $236.45   $236.40  
  Purchase #3 $162.70   7.181%   $174.3835   $174.38   $174.40   $174.40  
  Purchase #4 $30.56   12.534%   $34.3904   $34.39   $34.40   $34.40  
  Purchase #5 $229.55   9.397%   $251.1208   $251.12   $251.10   $251.10  
  Purchase #6 $205.67   7.700%   $221.5066   $221.51   $221.50   $221.50  
  Purchase #7 $245.78   11.779%   $274.7304   $274.73   $274.75   $274.70  
  7 purchase totals = $1,191.99       $1,310.5243   $1,310.52   $1,310.55   $1,310.50