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 $49.88   10.224%   $54.9797   $54.98   $55.00   $55.00  
  Purchase #2 $52.38   13.398%   $59.3979   $59.40   $59.40   $59.40  
  Purchase #3 $184.83   13.184%   $209.198   $209.20   $209.20   $209.20  
  Purchase #4 $238.76   12.805%   $269.3332   $269.33   $269.35   $269.30  
  Purchase #5 $191.73   11.449%   $213.6812   $213.68   $213.70   $213.70  
  Purchase #6 $72.76   13.424%   $82.5273   $82.53   $82.55   $82.50  
  Purchase #7 $157.71   3.487%   $163.2093   $163.21   $163.20   $163.20  
  7 purchase totals = $948.05       $1,052.3266   $1,052.33   $1,052.40   $1,052.30