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 $96.43   8.571%   $104.695   $104.70   $104.70   $104.70  
  Purchase #2 $8.87   7.109%   $9.5006   $9.50   $9.50   $9.50  
  Purchase #3 $103.86   5.792%   $109.8756   $109.88   $109.90   $109.90  
  Purchase #4 $170.28   8.345%   $184.4899   $184.49   $184.50   $184.50  
  Purchase #5 $148.35   8.308%   $160.6749   $160.67   $160.65   $160.70  
  Purchase #6 $171.28   9.167%   $186.9812   $186.98   $187.00   $187.00  
  Purchase #7 $58.55   5.419%   $61.7228   $61.72   $61.70   $61.70  
  7 purchase totals = $757.62       $817.9400   $817.94   $817.95   $818.00