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 $247.32   11.567%   $275.9275   $275.93   $275.95   $275.90  
  Purchase #2 $98.57   13.475%   $111.8523   $111.85   $111.85   $111.90  
  Purchase #3 $229.69   3.860%   $238.556   $238.56   $238.55   $238.60  
  Purchase #4 $52.38   8.130%   $56.6385   $56.64   $56.65   $56.60  
  Purchase #5 $43.92   4.677%   $45.9741   $45.97   $45.95   $46.00  
  Purchase #6 $144.53   3.477%   $149.5553   $149.56   $149.55   $149.60  
  Purchase #7 $204.63   12.542%   $230.2947   $230.29   $230.30   $230.30  
  7 purchase totals = $1,021.04       $1,108.7984   $1,108.80   $1,108.80   $1,108.90