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 $98.67   4.620%   $103.2286   $103.23   $103.25   $103.20  
  Purchase #2 $134.74   11.572%   $150.3321   $150.33   $150.35   $150.30  
  Purchase #3 $54.81   13.297%   $62.0981   $62.10   $62.10   $62.10  
  Purchase #4 $44.93   10.473%   $49.6355   $49.64   $49.65   $49.60  
  Purchase #5 $141.52   10.866%   $156.8976   $156.90   $156.90   $156.90  
  Purchase #6 $156.71   4.407%   $163.6162   $163.62   $163.60   $163.60  
  Purchase #7 $243.62   9.722%   $267.3047   $267.30   $267.30   $267.30  
  7 purchase totals = $875.00       $953.1128   $953.12   $953.15   $953.00