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 $186.94   4.301%   $194.9803   $194.98   $195.00   $195.00  
  Purchase #2 $144.39   7.464%   $155.1673   $155.17   $155.15   $155.20  
  Purchase #3 $76.33   3.824%   $79.2489   $79.25   $79.25   $79.20  
  Purchase #4 $192.53   12.173%   $215.9667   $215.97   $215.95   $216.00  
  Purchase #5 $20.87   13.635%   $23.7156   $23.72   $23.70   $23.70  
  Purchase #6 $39.37   10.846%   $43.6401   $43.64   $43.65   $43.60  
  Purchase #7 $205.92   3.143%   $212.3921   $212.39   $212.40   $212.40  
  7 purchase totals = $866.35       $925.1110   $925.12   $925.10   $925.10