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 $247.77   11.323%   $275.825   $275.83   $275.85   $275.80  
  Purchase #2 $67.76   5.445%   $71.4495   $71.45   $71.45   $71.40  
  Purchase #3 $68.67   4.826%   $71.984   $71.98   $72.00   $72.00  
  Purchase #4 $5.44   5.453%   $5.7366   $5.74   $5.75   $5.70  
  Purchase #5 $165.65   7.185%   $177.552   $177.55   $177.55   $177.60  
  Purchase #6 $133.87   13.694%   $152.2022   $152.20   $152.20   $152.20  
  Purchase #7 $164.43   13.817%   $187.1493   $187.15   $187.15   $187.10  
  7 purchase totals = $853.59       $941.8986   $941.90   $941.95   $941.80