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 $63.28   5.619%   $66.8357   $66.84   $66.85   $66.80  
  Purchase #2 $235.70   3.817%   $244.6967   $244.70   $244.70   $244.70  
  Purchase #3 $80.76   12.218%   $90.6273   $90.63   $90.65   $90.60  
  Purchase #4 $64.90   5.424%   $68.4202   $68.42   $68.40   $68.40  
  Purchase #5 $129.55   13.137%   $146.569   $146.57   $146.55   $146.60  
  Purchase #6 $50.33   12.373%   $56.5573   $56.56   $56.55   $56.60  
  Purchase #7 $114.95   8.282%   $124.4702   $124.47   $124.45   $124.50  
  7 purchase totals = $739.47       $798.1764   $798.19   $798.15   $798.20