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 $132.50   11.271%   $147.4341   $147.43   $147.45   $147.40  
  Purchase #2 $150.35   6.274%   $159.783   $159.78   $159.80   $159.80  
  Purchase #3 $132.70   12.206%   $148.8974   $148.90   $148.90   $148.90  
  Purchase #4 $149.59   3.698%   $155.1218   $155.12   $155.10   $155.10  
  Purchase #5 $206.42   12.341%   $231.8943   $231.89   $231.90   $231.90  
  Purchase #6 $15.41   7.543%   $16.5724   $16.57   $16.55   $16.60  
  Purchase #7 $100.30   3.113%   $103.4223   $103.42   $103.40   $103.40  
  7 purchase totals = $887.27       $963.1253   $963.11   $963.10   $963.10