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 $87.47   6.329%   $93.006   $93.01   $93.00   $93.00  
  Purchase #2 $112.89   13.690%   $128.3446   $128.34   $128.35   $128.30  
  Purchase #3 $19.58   3.589%   $20.2827   $20.28   $20.30   $20.30  
  Purchase #4 $142.32   10.549%   $157.3333   $157.33   $157.35   $157.30  
  Purchase #5 $152.54   9.257%   $166.6606   $166.66   $166.65   $166.70  
  Purchase #6 $213.59   6.179%   $226.7877   $226.79   $226.80   $226.80  
  Purchase #7 $173.37   4.761%   $181.6241   $181.62   $181.60   $181.60  
  7 purchase totals = $901.76       $974.0390   $974.03   $974.05   $974.00