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 $219.48   12.152%   $246.1512   $246.15   $246.15   $246.20  
  Purchase #2 $247.33   10.578%   $273.4926   $273.49   $273.50   $273.50  
  Purchase #3 $223.27   7.744%   $240.56   $240.56   $240.55   $240.60  
  Purchase #4 $33.29   9.316%   $36.3913   $36.39   $36.40   $36.40  
  Purchase #5 $63.29   11.407%   $70.5095   $70.51   $70.50   $70.50  
  Purchase #6 $17.83   6.275%   $18.9488   $18.95   $18.95   $18.90  
  Purchase #7 $149.70   8.667%   $162.6745   $162.67   $162.65   $162.70  
  7 purchase totals = $954.19       $1,048.7279   $1,048.72   $1,048.70   $1,048.80