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 $63.74   7.399%   $68.4561   $68.46   $68.45   $68.50  
  Purchase #2 $98.53   8.822%   $107.2223   $107.22   $107.20   $107.20  
  Purchase #3 $240.38   5.115%   $252.6754   $252.68   $252.70   $252.70  
  Purchase #4 $97.62   5.818%   $103.2995   $103.30   $103.30   $103.30  
  Purchase #5 $144.44   5.464%   $152.3322   $152.33   $152.35   $152.30  
  Purchase #6 $48.90   7.827%   $52.7274   $52.73   $52.75   $52.70  
  Purchase #7 $22.65   9.641%   $24.8337   $24.83   $24.85   $24.80  
  7 purchase totals = $716.26       $761.5466   $761.55   $761.60   $761.50