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 $105.68   10.267%   $116.5302   $116.53   $116.55   $116.50  
  Purchase #2 $34.42   6.447%   $36.6391   $36.64   $36.65   $36.60  
  Purchase #3 $83.74   5.443%   $88.298   $88.30   $88.30   $88.30  
  Purchase #4 $166.88   4.542%   $174.4597   $174.46   $174.45   $174.50  
  Purchase #5 $11.88   6.780%   $12.6855   $12.69   $12.70   $12.70  
  Purchase #6 $82.94   13.694%   $94.2978   $94.30   $94.30   $94.30  
  Purchase #7 $228.45   5.785%   $241.6658   $241.67   $241.65   $241.70  
  7 purchase totals = $713.99       $764.5761   $764.59   $764.60   $764.60