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 $92.39   5.681%   $97.6387   $97.64   $97.65   $97.60  
  Purchase #2 $85.59   7.191%   $91.7448   $91.74   $91.75   $91.70  
  Purchase #3 $165.42   11.430%   $184.3275   $184.33   $184.35   $184.30  
  Purchase #4 $75.71   9.392%   $82.8207   $82.82   $82.80   $82.80  
  Purchase #5 $17.54   4.576%   $18.3426   $18.34   $18.35   $18.30  
  Purchase #6 $14.64   12.275%   $16.4371   $16.44   $16.45   $16.40  
  Purchase #7 $102.70   3.420%   $106.2123   $106.21   $106.20   $106.20  
  7 purchase totals = $553.99       $597.5237   $597.52   $597.55   $597.30