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 $87.55   7.259%   $93.9053   $93.91   $93.90   $93.90  
  Purchase #2 $174.92   12.729%   $197.1856   $197.19   $197.20   $197.20  
  Purchase #3 $36.60   6.343%   $38.9215   $38.92   $38.90   $38.90  
  Purchase #4 $23.36   5.181%   $24.5703   $24.57   $24.55   $24.60  
  Purchase #5 $235.48   7.186%   $252.4016   $252.40   $252.40   $252.40  
  Purchase #6 $174.59   12.837%   $197.0021   $197.00   $197.00   $197.00  
  Purchase #7 $18.54   4.294%   $19.3361   $19.34   $19.35   $19.30  
  7 purchase totals = $751.04       $823.3225   $823.33   $823.30   $823.30