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 $241.70   8.595%   $262.4741   $262.47   $262.45   $262.50  
  Purchase #2 $62.96   10.814%   $69.7685   $69.77   $69.75   $69.80  
  Purchase #3 $210.38   13.449%   $238.674   $238.67   $238.65   $238.70  
  Purchase #4 $35.51   12.174%   $39.833   $39.83   $39.85   $39.80  
  Purchase #5 $211.46   5.812%   $223.7501   $223.75   $223.75   $223.80  
  Purchase #6 $111.31   12.846%   $125.6089   $125.61   $125.60   $125.60  
  Purchase #7 $74.71   9.156%   $81.5504   $81.55   $81.55   $81.60  
  7 purchase totals = $948.03       $1,041.6590   $1,041.65   $1,041.60   $1,041.80