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 $233.82   5.319%   $246.2569   $246.26   $246.25   $246.30  
  Purchase #2 $149.86   13.865%   $170.6381   $170.64   $170.65   $170.60  
  Purchase #3 $132.65   8.190%   $143.514   $143.51   $143.50   $143.50  
  Purchase #4 $240.67   10.814%   $266.6961   $266.70   $266.70   $266.70  
  Purchase #5 $167.60   4.712%   $175.4973   $175.50   $175.50   $175.50  
  Purchase #6 $187.84   12.438%   $211.2035   $211.20   $211.20   $211.20  
  Purchase #7 $70.34   3.779%   $72.9981   $73.00   $73.00   $73.00  
  7 purchase totals = $1,182.78       $1,286.8040   $1,286.81   $1,286.80   $1,286.80