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 $58.68   3.234%   $60.5777   $60.58   $60.60   $60.60  
  Purchase #2 $151.31   11.276%   $168.3717   $168.37   $168.35   $168.40  
  Purchase #3 $72.96   9.762%   $80.0824   $80.08   $80.10   $80.10  
  Purchase #4 $148.80   7.551%   $160.0359   $160.04   $160.05   $160.00  
  Purchase #5 $131.79   12.504%   $148.269   $148.27   $148.25   $148.30  
  Purchase #6 $112.72   3.506%   $116.672   $116.67   $116.65   $116.70  
  Purchase #7 $167.86   6.452%   $178.6903   $178.69   $178.70   $178.70  
  7 purchase totals = $844.12       $912.6990   $912.70   $912.70   $912.80