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 $212.63   13.687%   $241.7327   $241.73   $241.75   $241.70  
  Purchase #2 $61.48   9.134%   $67.0956   $67.10   $67.10   $67.10  
  Purchase #3 $183.48   8.676%   $199.3987   $199.40   $199.40   $199.40  
  Purchase #4 $165.38   7.340%   $177.5189   $177.52   $177.50   $177.50  
  Purchase #5 $182.41   9.397%   $199.5511   $199.55   $199.55   $199.60  
  Purchase #6 $87.59   7.487%   $94.1479   $94.15   $94.15   $94.10  
  Purchase #7 $243.56   10.515%   $269.1703   $269.17   $269.15   $269.20  
  7 purchase totals = $1,136.53       $1,248.6152   $1,248.62   $1,248.60   $1,248.60