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 $173.66   13.234%   $196.6422   $196.64   $196.65   $196.60  
  Purchase #2 $238.77   11.458%   $266.1283   $266.13   $266.15   $266.10  
  Purchase #3 $31.72   12.111%   $35.5616   $35.56   $35.55   $35.60  
  Purchase #4 $131.36   5.299%   $138.3208   $138.32   $138.30   $138.30  
  Purchase #5 $245.97   12.622%   $277.0163   $277.02   $277.00   $277.00  
  Purchase #6 $231.48   10.491%   $255.7646   $255.76   $255.75   $255.80  
  Purchase #7 $48.30   11.787%   $53.9931   $53.99   $54.00   $54.00  
  7 purchase totals = $1,101.26       $1,223.4269   $1,223.42   $1,223.40   $1,223.40