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 $65.41   3.238%   $67.528   $67.53   $67.55   $67.50  
  Purchase #2 $220.59   5.606%   $232.9563   $232.96   $232.95   $233.00  
  Purchase #3 $210.33   10.695%   $232.8248   $232.82   $232.80   $232.80  
  Purchase #4 $80.59   13.642%   $91.5841   $91.58   $91.60   $91.60  
  Purchase #5 $69.41   10.328%   $76.5787   $76.58   $76.60   $76.60  
  Purchase #6 $74.66   4.289%   $77.8622   $77.86   $77.85   $77.90  
  Purchase #7 $21.29   5.754%   $22.515   $22.52   $22.50   $22.50  
  7 purchase totals = $742.28       $801.8491   $801.85   $801.85   $801.90