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 $53.39   6.198%   $56.6991   $56.70   $56.70   $56.70  
  Purchase #2 $88.97   10.629%   $98.4266   $98.43   $98.45   $98.40  
  Purchase #3 $242.56   4.550%   $253.5965   $253.60   $253.60   $253.60  
  Purchase #4 $77.99   11.222%   $86.742   $86.74   $86.75   $86.70  
  Purchase #5 $191.98   12.806%   $216.565   $216.57   $216.55   $216.60  
  Purchase #6 $217.27   10.614%   $240.331   $240.33   $240.35   $240.30  
  Purchase #7 $100.43   4.304%   $104.7525   $104.75   $104.75   $104.80  
  7 purchase totals = $972.59       $1,057.1127   $1,057.12   $1,057.15   $1,057.10