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 $141.26   9.763%   $155.0512   $155.05   $155.05   $155.10  
  Purchase #2 $240.84   6.233%   $255.8516   $255.85   $255.85   $255.90  
  Purchase #3 $139.47   13.584%   $158.4156   $158.42   $158.40   $158.40  
  Purchase #4 $72.52   4.294%   $75.634   $75.63   $75.65   $75.60  
  Purchase #5 $43.27   13.864%   $49.269   $49.27   $49.25   $49.30  
  Purchase #6 $227.39   11.847%   $254.3289   $254.33   $254.35   $254.30  
  Purchase #7 $32.98   12.536%   $37.1144   $37.11   $37.10   $37.10  
  7 purchase totals = $897.73       $985.6647   $985.66   $985.65   $985.70