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 $54.79   12.259%   $61.5067   $61.51   $61.50   $61.50  
  Purchase #2 $189.55   9.512%   $207.58   $207.58   $207.60   $207.60  
  Purchase #3 $95.67   4.615%   $100.0852   $100.09   $100.10   $100.10  
  Purchase #4 $60.94   12.655%   $68.652   $68.65   $68.65   $68.70  
  Purchase #5 $8.73   9.668%   $9.574   $9.57   $9.55   $9.60  
  Purchase #6 $20.63   4.863%   $21.6332   $21.63   $21.65   $21.60  
  Purchase #7 $85.76   10.525%   $94.7862   $94.79   $94.80   $94.80  
  7 purchase totals = $516.07       $563.8173   $563.82   $563.85   $563.90