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 $129.94   12.304%   $145.9278   $145.93   $145.95   $145.90  
  Purchase #2 $23.97   3.544%   $24.8195   $24.82   $24.80   $24.80  
  Purchase #3 $137.95   13.303%   $156.3015   $156.30   $156.30   $156.30  
  Purchase #4 $244.49   6.490%   $260.3574   $260.36   $260.35   $260.40  
  Purchase #5 $205.98   3.827%   $213.8629   $213.86   $213.85   $213.90  
  Purchase #6 $140.96   8.249%   $152.5878   $152.59   $152.60   $152.60  
  Purchase #7 $12.82   9.585%   $14.0488   $14.05   $14.05   $14.00  
  7 purchase totals = $896.11       $967.9057   $967.91   $967.90   $967.90