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 $205.79   8.699%   $223.6917   $223.69   $223.70   $223.70  
  Purchase #2 $191.64   11.644%   $213.9546   $213.95   $213.95   $214.00  
  Purchase #3 $6.39   12.417%   $7.1834   $7.18   $7.20   $7.20  
  Purchase #4 $153.52   11.545%   $171.2439   $171.24   $171.25   $171.20  
  Purchase #5 $91.70   3.628%   $95.0269   $95.03   $95.05   $95.00  
  Purchase #6 $98.82   6.750%   $105.4904   $105.49   $105.50   $105.50  
  Purchase #7 $191.34   12.332%   $214.936   $214.94   $214.95   $214.90  
  7 purchase totals = $939.20       $1,031.5269   $1,031.52   $1,031.60   $1,031.50