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 $44.96   8.662%   $48.8544   $48.85   $48.85   $48.90  
  Purchase #2 $236.95   9.368%   $259.1475   $259.15   $259.15   $259.10  
  Purchase #3 $13.35   6.561%   $14.2259   $14.23   $14.25   $14.20  
  Purchase #4 $162.98   4.234%   $169.8806   $169.88   $169.90   $169.90  
  Purchase #5 $10.51   7.545%   $11.303   $11.30   $11.30   $11.30  
  Purchase #6 $218.30   8.180%   $236.1569   $236.16   $236.15   $236.20  
  Purchase #7 $243.76   4.466%   $254.6463   $254.65   $254.65   $254.60  
  7 purchase totals = $930.81       $994.2146   $994.22   $994.25   $994.20