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 $96.88   9.347%   $105.9354   $105.94   $105.95   $105.90  
  Purchase #2 $165.74   5.765%   $175.2949   $175.29   $175.30   $175.30  
  Purchase #3 $91.56   3.652%   $94.9038   $94.90   $94.90   $94.90  
  Purchase #4 $244.86   11.291%   $272.5071   $272.51   $272.50   $272.50  
  Purchase #5 $85.53   6.385%   $90.9911   $90.99   $91.00   $91.00  
  Purchase #6 $76.43   10.796%   $84.6814   $84.68   $84.70   $84.70  
  Purchase #7 $216.29   5.754%   $228.7353   $228.74   $228.75   $228.70  
  7 purchase totals = $977.29       $1,053.0490   $1,053.05   $1,053.10   $1,053.00