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 $95.31   9.601%   $104.4607   $104.46   $104.45   $104.50  
  Purchase #2 $5.85   13.551%   $6.6427   $6.64   $6.65   $6.60  
  Purchase #3 $170.44   11.587%   $190.1889   $190.19   $190.20   $190.20  
  Purchase #4 $26.89   6.855%   $28.7333   $28.73   $28.75   $28.70  
  Purchase #5 $239.55   13.123%   $270.9861   $270.99   $271.00   $271.00  
  Purchase #6 $165.90   5.472%   $174.978   $174.98   $175.00   $175.00  
  Purchase #7 $247.65   12.319%   $278.158   $278.16   $278.15   $278.20  
  7 purchase totals = $951.59       $1,054.1477   $1,054.15   $1,054.20   $1,054.20