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 $94.88   6.666%   $101.2047   $101.20   $101.20   $101.20  
  Purchase #2 $246.53   4.506%   $257.6386   $257.64   $257.65   $257.60  
  Purchase #3 $161.30   3.677%   $167.231   $167.23   $167.25   $167.20  
  Purchase #4 $192.84   8.705%   $209.6267   $209.63   $209.65   $209.60  
  Purchase #5 $217.61   9.682%   $238.679   $238.68   $238.70   $238.70  
  Purchase #6 $51.27   13.817%   $58.354   $58.35   $58.35   $58.40  
  Purchase #7 $171.51   5.674%   $181.2415   $181.24   $181.25   $181.20  
  7 purchase totals = $1,135.94       $1,213.9755   $1,213.97   $1,214.05   $1,213.90