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 $155.47   12.574%   $175.0188   $175.02   $175.00   $175.00  
  Purchase #2 $148.36   9.418%   $162.3325   $162.33   $162.35   $162.30  
  Purchase #3 $238.82   7.209%   $256.0365   $256.04   $256.05   $256.00  
  Purchase #4 $126.33   8.291%   $136.804   $136.80   $136.80   $136.80  
  Purchase #5 $6.55   9.249%   $7.1558   $7.16   $7.15   $7.20  
  Purchase #6 $196.31   3.564%   $203.3065   $203.31   $203.30   $203.30  
  Purchase #7 $144.99   6.219%   $154.0069   $154.01   $154.00   $154.00  
  7 purchase totals = $1,016.83       $1,094.6610   $1,094.67   $1,094.65   $1,094.60