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 $90.56   12.211%   $101.6183   $101.62   $101.60   $101.60  
  Purchase #2 $88.62   10.751%   $98.1475   $98.15   $98.15   $98.10  
  Purchase #3 $166.55   4.786%   $174.5211   $174.52   $174.50   $174.50  
  Purchase #4 $56.54   9.141%   $61.7083   $61.71   $61.70   $61.70  
  Purchase #5 $61.54   10.432%   $67.9599   $67.96   $67.95   $68.00  
  Purchase #6 $183.80   10.174%   $202.4998   $202.50   $202.50   $202.50  
  Purchase #7 $248.54   5.686%   $262.672   $262.67   $262.65   $262.70  
  7 purchase totals = $896.15       $969.1269   $969.13   $969.05   $969.10