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 $54.41   10.872%   $60.3255   $60.33   $60.35   $60.30  
  Purchase #2 $83.93   9.103%   $91.5701   $91.57   $91.55   $91.60  
  Purchase #3 $180.30   12.610%   $203.0358   $203.04   $203.05   $203.00  
  Purchase #4 $14.36   13.205%   $16.2562   $16.26   $16.25   $16.30  
  Purchase #5 $159.52   4.809%   $167.1913   $167.19   $167.20   $167.20  
  Purchase #6 $87.37   11.533%   $97.4464   $97.45   $97.45   $97.40  
  Purchase #7 $49.74   3.398%   $51.4302   $51.43   $51.45   $51.40  
  7 purchase totals = $629.63       $687.2555   $687.27   $687.30   $687.20