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 $212.43   13.591%   $241.3014   $241.30   $241.30   $241.30  
  Purchase #2 $110.85   8.423%   $120.1869   $120.19   $120.20   $120.20  
  Purchase #3 $132.26   11.379%   $147.3099   $147.31   $147.30   $147.30  
  Purchase #4 $37.59   12.399%   $42.2508   $42.25   $42.25   $42.30  
  Purchase #5 $19.52   10.509%   $21.5714   $21.57   $21.55   $21.60  
  Purchase #6 $179.66   6.607%   $191.5301   $191.53   $191.55   $191.50  
  Purchase #7 $25.63   11.651%   $28.6162   $28.62   $28.60   $28.60  
  7 purchase totals = $717.94       $792.7667   $792.77   $792.75   $792.80