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 $54.73   13.651%   $62.2012   $62.20   $62.20   $62.20  
  Purchase #2 $127.69   12.601%   $143.7802   $143.78   $143.80   $143.80  
  Purchase #3 $83.27   9.482%   $91.1657   $91.17   $91.15   $91.20  
  Purchase #4 $174.88   11.565%   $195.1049   $195.10   $195.10   $195.10  
  Purchase #5 $45.59   10.723%   $50.4786   $50.48   $50.50   $50.50  
  Purchase #6 $26.87   3.825%   $27.8978   $27.90   $27.90   $27.90  
  Purchase #7 $110.84   8.850%   $120.6493   $120.65   $120.65   $120.60  
  7 purchase totals = $623.87       $691.2777   $691.28   $691.30   $691.30