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 $240.97   4.592%   $252.0353   $252.04   $252.05   $252.00  
  Purchase #2 $153.76   13.366%   $174.3116   $174.31   $174.30   $174.30  
  Purchase #3 $216.81   4.212%   $225.942   $225.94   $225.95   $225.90  
  Purchase #4 $110.40   11.727%   $123.3466   $123.35   $123.35   $123.30  
  Purchase #5 $141.41   10.224%   $155.8678   $155.87   $155.85   $155.90  
  Purchase #6 $36.81   6.770%   $39.302   $39.30   $39.30   $39.30  
  Purchase #7 $62.64   6.197%   $66.5218   $66.52   $66.50   $66.50  
  7 purchase totals = $962.80       $1,037.3271   $1,037.33   $1,037.30   $1,037.20