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 $67.67   11.722%   $75.6023   $75.60   $75.60   $75.60  
  Purchase #2 $171.78   9.422%   $187.9651   $187.97   $187.95   $188.00  
  Purchase #3 $222.74   10.500%   $246.1277   $246.13   $246.15   $246.10  
  Purchase #4 $160.41   10.393%   $177.0814   $177.08   $177.10   $177.10  
  Purchase #5 $17.45   11.645%   $19.4821   $19.48   $19.50   $19.50  
  Purchase #6 $206.97   3.249%   $213.6945   $213.69   $213.70   $213.70  
  Purchase #7 $38.85   4.557%   $40.6204   $40.62   $40.60   $40.60  
  7 purchase totals = $885.87       $960.5735   $960.57   $960.60   $960.60