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 $229.75   5.831%   $243.1467   $243.15   $243.15   $243.10  
  Purchase #2 $10.57   13.251%   $11.9706   $11.97   $11.95   $12.00  
  Purchase #3 $175.45   4.817%   $183.9014   $183.90   $183.90   $183.90  
  Purchase #4 $235.49   10.118%   $259.3169   $259.32   $259.30   $259.30  
  Purchase #5 $10.29   5.142%   $10.8191   $10.82   $10.80   $10.80  
  Purchase #6 $124.72   6.654%   $133.0189   $133.02   $133.00   $133.00  
  Purchase #7 $96.70   13.281%   $109.5427   $109.54   $109.55   $109.50  
  7 purchase totals = $882.97       $951.7163   $951.72   $951.65   $951.60