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 $39.68   3.616%   $41.1148   $41.11   $41.10   $41.10  
  Purchase #2 $68.44   11.695%   $76.4441   $76.44   $76.45   $76.40  
  Purchase #3 $238.84   12.662%   $269.0819   $269.08   $269.10   $269.10  
  Purchase #4 $44.34   9.409%   $48.512   $48.51   $48.50   $48.50  
  Purchase #5 $239.57   9.140%   $261.4667   $261.47   $261.45   $261.50  
  Purchase #6 $198.94   4.215%   $207.3253   $207.33   $207.35   $207.30  
  Purchase #7 $107.74   11.702%   $120.3477   $120.35   $120.35   $120.30  
  7 purchase totals = $937.55       $1,024.2925   $1,024.29   $1,024.30   $1,024.20