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 $52.78   11.707%   $58.959   $58.96   $58.95   $59.00  
  Purchase #2 $140.52   6.692%   $149.9236   $149.92   $149.90   $149.90  
  Purchase #3 $147.96   8.714%   $160.8532   $160.85   $160.85   $160.90  
  Purchase #4 $126.62   10.399%   $139.7872   $139.79   $139.80   $139.80  
  Purchase #5 $51.64   8.492%   $56.0253   $56.03   $56.05   $56.00  
  Purchase #6 $196.77   4.706%   $206.03   $206.03   $206.05   $206.00  
  Purchase #7 $188.68   13.196%   $213.5782   $213.58   $213.60   $213.60  
  7 purchase totals = $904.97       $985.1565   $985.16   $985.20   $985.20