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 $141.82   11.144%   $157.6244   $157.62   $157.60   $157.60  
  Purchase #2 $244.50   13.686%   $277.9623   $277.96   $277.95   $278.00  
  Purchase #3 $39.55   9.449%   $43.2871   $43.29   $43.30   $43.30  
  Purchase #4 $12.67   12.216%   $14.2178   $14.22   $14.20   $14.20  
  Purchase #5 $59.71   9.657%   $65.4762   $65.48   $65.50   $65.50  
  Purchase #6 $69.30   12.127%   $77.704   $77.70   $77.70   $77.70  
  Purchase #7 $218.32   11.827%   $244.1407   $244.14   $244.15   $244.10  
  7 purchase totals = $785.87       $880.4125   $880.41   $880.40   $880.40