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 $86.61   8.251%   $93.7562   $93.76   $93.75   $93.80  
  Purchase #2 $94.58   12.385%   $106.2937   $106.29   $106.30   $106.30  
  Purchase #3 $12.35   11.627%   $13.7859   $13.79   $13.80   $13.80  
  Purchase #4 $248.79   9.225%   $271.7409   $271.74   $271.75   $271.70  
  Purchase #5 $60.87   6.179%   $64.6312   $64.63   $64.65   $64.60  
  Purchase #6 $34.65   7.349%   $37.1964   $37.20   $37.20   $37.20  
  Purchase #7 $17.52   11.384%   $19.5145   $19.51   $19.50   $19.50  
  7 purchase totals = $555.37       $606.9188   $606.92   $606.95   $606.90