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 $203.95   12.195%   $228.8217   $228.82   $228.80   $228.80  
  Purchase #2 $56.79   5.437%   $59.8777   $59.88   $59.90   $59.90  
  Purchase #3 $62.90   3.298%   $64.9744   $64.97   $64.95   $65.00  
  Purchase #4 $242.51   8.181%   $262.3497   $262.35   $262.35   $262.30  
  Purchase #5 $176.36   3.755%   $182.9823   $182.98   $183.00   $183.00  
  Purchase #6 $12.27   9.139%   $13.3914   $13.39   $13.40   $13.40  
  Purchase #7 $201.85   11.803%   $225.6744   $225.67   $225.65   $225.70  
  7 purchase totals = $956.63       $1,038.0716   $1,038.06   $1,038.05   $1,038.10