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 $168.92   3.152%   $174.2444   $174.24   $174.25   $174.20  
  Purchase #2 $24.65   11.852%   $27.5715   $27.57   $27.55   $27.60  
  Purchase #3 $189.88   11.846%   $212.3732   $212.37   $212.35   $212.40  
  Purchase #4 $22.97   10.136%   $25.2982   $25.30   $25.30   $25.30  
  Purchase #5 $184.35   9.187%   $201.2862   $201.29   $201.30   $201.30  
  Purchase #6 $69.53   4.327%   $72.5386   $72.54   $72.55   $72.50  
  Purchase #7 $62.68   9.143%   $68.4108   $68.41   $68.40   $68.40  
  7 purchase totals = $722.98       $781.7229   $781.72   $781.70   $781.70