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 $50.65   10.494%   $55.9652   $55.97   $55.95   $56.00  
  Purchase #2 $99.54   7.449%   $106.9547   $106.95   $106.95   $107.00  
  Purchase #3 $165.31   8.180%   $178.8324   $178.83   $178.85   $178.80  
  Purchase #4 $213.46   5.225%   $224.6133   $224.61   $224.60   $224.60  
  Purchase #5 $126.58   7.318%   $135.8431   $135.84   $135.85   $135.80  
  Purchase #6 $133.29   8.538%   $144.6703   $144.67   $144.65   $144.70  
  Purchase #7 $110.73   9.170%   $120.8839   $120.88   $120.90   $120.90  
  7 purchase totals = $899.56       $967.7629   $967.75   $967.75   $967.80