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 $19.78   10.534%   $21.8636   $21.86   $21.85   $21.90  
  Purchase #2 $41.84   3.280%   $43.2124   $43.21   $43.20   $43.20  
  Purchase #3 $102.79   9.763%   $112.8254   $112.83   $112.85   $112.80  
  Purchase #4 $183.45   8.600%   $199.2267   $199.23   $199.25   $199.20  
  Purchase #5 $208.87   9.516%   $228.7461   $228.75   $228.75   $228.70  
  Purchase #6 $105.98   9.136%   $115.6623   $115.66   $115.65   $115.70  
  Purchase #7 $87.75   10.200%   $96.7005   $96.70   $96.70   $96.70  
  7 purchase totals = $750.46       $818.2370   $818.24   $818.25   $818.20