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 $95.54   6.471%   $101.7224   $101.72   $101.70   $101.70  
  Purchase #2 $44.96   8.244%   $48.6665   $48.67   $48.65   $48.70  
  Purchase #3 $24.52   6.435%   $26.0979   $26.10   $26.10   $26.10  
  Purchase #4 $50.36   5.840%   $53.301   $53.30   $53.30   $53.30  
  Purchase #5 $240.91   11.535%   $268.699   $268.70   $268.70   $268.70  
  Purchase #6 $109.31   4.573%   $114.3087   $114.31   $114.30   $114.30  
  Purchase #7 $9.84   6.194%   $10.4495   $10.45   $10.45   $10.40  
  7 purchase totals = $575.44       $623.2450   $623.25   $623.20   $623.20