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 $193.67   4.751%   $202.8713   $202.87   $202.85   $202.90  
  Purchase #2 $57.98   5.210%   $61.0008   $61.00   $61.00   $61.00  
  Purchase #3 $200.79   7.316%   $215.4798   $215.48   $215.50   $215.50  
  Purchase #4 $63.48   9.720%   $69.6503   $69.65   $69.65   $69.70  
  Purchase #5 $75.49   9.351%   $82.5491   $82.55   $82.55   $82.50  
  Purchase #6 $170.45   9.838%   $187.2189   $187.22   $187.20   $187.20  
  Purchase #7 $185.61   9.839%   $203.8722   $203.87   $203.85   $203.90  
  7 purchase totals = $947.47       $1,022.6424   $1,022.64   $1,022.60   $1,022.70