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 $66.93   3.531%   $69.2933   $69.29   $69.30   $69.30  
  Purchase #2 $210.97   9.650%   $231.3286   $231.33   $231.35   $231.30  
  Purchase #3 $241.33   11.790%   $269.7828   $269.78   $269.80   $269.80  
  Purchase #4 $233.55   3.541%   $241.82   $241.82   $241.80   $241.80  
  Purchase #5 $20.94   8.472%   $22.714   $22.71   $22.70   $22.70  
  Purchase #6 $20.95   3.222%   $21.625   $21.63   $21.65   $21.60  
  Purchase #7 $75.34   7.874%   $81.2723   $81.27   $81.25   $81.30  
  7 purchase totals = $870.01       $937.8360   $937.83   $937.85   $937.80