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 $59.65   6.161%   $63.325   $63.33   $63.35   $63.30  
  Purchase #2 $242.45   13.505%   $275.1929   $275.19   $275.20   $275.20  
  Purchase #3 $44.29   11.793%   $49.5131   $49.51   $49.50   $49.50  
  Purchase #4 $194.82   13.560%   $221.2376   $221.24   $221.25   $221.20  
  Purchase #5 $205.40   3.207%   $211.9872   $211.99   $212.00   $212.00  
  Purchase #6 $72.48   4.690%   $75.8793   $75.88   $75.90   $75.90  
  Purchase #7 $66.81   6.362%   $71.0605   $71.06   $71.05   $71.10  
  7 purchase totals = $885.90       $968.1956   $968.20   $968.25   $968.20