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 $95.44   6.861%   $101.9881   $101.99   $102.00   $102.00  
  Purchase #2 $128.85   9.312%   $140.8485   $140.85   $140.85   $140.80  
  Purchase #3 $75.91   5.780%   $80.2976   $80.30   $80.30   $80.30  
  Purchase #4 $117.86   12.327%   $132.3886   $132.39   $132.40   $132.40  
  Purchase #5 $102.77   6.688%   $109.6433   $109.64   $109.65   $109.60  
  Purchase #6 $194.63   3.517%   $201.4751   $201.48   $201.50   $201.50  
  Purchase #7 $119.93   5.693%   $126.7576   $126.76   $126.75   $126.80  
  7 purchase totals = $835.39       $893.3988   $893.41   $893.45   $893.40