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 $161.47   5.145%   $169.7776   $169.78   $169.80   $169.80  
  Purchase #2 $40.65   12.305%   $45.652   $45.65   $45.65   $45.70  
  Purchase #3 $64.29   6.437%   $68.4283   $68.43   $68.45   $68.40  
  Purchase #4 $13.33   6.158%   $14.1509   $14.15   $14.15   $14.20  
  Purchase #5 $188.74   12.551%   $212.4288   $212.43   $212.45   $212.40  
  Purchase #6 $72.70   3.768%   $75.4393   $75.44   $75.45   $75.40  
  Purchase #7 $50.64   13.210%   $57.3295   $57.33   $57.35   $57.30  
  7 purchase totals = $591.82       $643.2064   $643.21   $643.30   $643.20