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 $222.78   9.299%   $243.4963   $243.50   $243.50   $243.50  
  Purchase #2 $66.95   5.432%   $70.5867   $70.59   $70.60   $70.60  
  Purchase #3 $56.89   3.532%   $58.8994   $58.90   $58.90   $58.90  
  Purchase #4 $165.47   3.358%   $171.0265   $171.03   $171.05   $171.00  
  Purchase #5 $41.48   12.281%   $46.5742   $46.57   $46.55   $46.60  
  Purchase #6 $225.48   4.747%   $236.1835   $236.18   $236.20   $236.20  
  Purchase #7 $120.73   10.700%   $133.6481   $133.65   $133.65   $133.60  
  7 purchase totals = $899.78       $960.4147   $960.42   $960.45   $960.40