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 $69.76   7.543%   $75.022   $75.02   $75.00   $75.00  
  Purchase #2 $234.35   4.393%   $244.645   $244.65   $244.65   $244.60  
  Purchase #3 $205.86   9.209%   $224.8176   $224.82   $224.80   $224.80  
  Purchase #4 $249.85   3.469%   $258.5173   $258.52   $258.50   $258.50  
  Purchase #5 $20.26   13.365%   $22.9677   $22.97   $22.95   $23.00  
  Purchase #6 $121.35   13.570%   $137.8172   $137.82   $137.80   $137.80  
  Purchase #7 $227.86   11.706%   $254.5333   $254.53   $254.55   $254.50  
  7 purchase totals = $1,129.29       $1,218.3201   $1,218.33   $1,218.25   $1,218.20