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 $232.55   5.859%   $246.1751   $246.18   $246.20   $246.20  
  Purchase #2 $61.86   6.529%   $65.8988   $65.90   $65.90   $65.90  
  Purchase #3 $89.49   4.656%   $93.6567   $93.66   $93.65   $93.70  
  Purchase #4 $239.52   11.405%   $266.8373   $266.84   $266.85   $266.80  
  Purchase #5 $64.46   11.390%   $71.802   $71.80   $71.80   $71.80  
  Purchase #6 $121.26   3.614%   $125.6423   $125.64   $125.65   $125.60  
  Purchase #7 $16.26   12.298%   $18.2597   $18.26   $18.25   $18.30  
  7 purchase totals = $825.40       $888.2719   $888.28   $888.30   $888.30