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 $149.79   11.692%   $167.3034   $167.30   $167.30   $167.30  
  Purchase #2 $117.82   5.448%   $124.2388   $124.24   $124.25   $124.20  
  Purchase #3 $49.28   7.331%   $52.8927   $52.89   $52.90   $52.90  
  Purchase #4 $211.50   3.530%   $218.966   $218.97   $218.95   $219.00  
  Purchase #5 $50.96   12.272%   $57.2138   $57.21   $57.20   $57.20  
  Purchase #6 $211.96   5.736%   $224.118   $224.12   $224.10   $224.10  
  Purchase #7 $16.59   4.697%   $17.3692   $17.37   $17.35   $17.40  
  7 purchase totals = $807.90       $862.1019   $862.10   $862.05   $862.10