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 $54.70   11.553%   $61.0195   $61.02   $61.00   $61.00  
  Purchase #2 $187.82   6.325%   $199.6996   $199.70   $199.70   $199.70  
  Purchase #3 $173.66   7.203%   $186.1687   $186.17   $186.15   $186.20  
  Purchase #4 $25.35   9.251%   $27.6951   $27.70   $27.70   $27.70  
  Purchase #5 $193.41   3.586%   $200.3457   $200.35   $200.35   $200.30  
  Purchase #6 $188.87   5.577%   $199.4033   $199.40   $199.40   $199.40  
  Purchase #7 $131.96   5.312%   $138.9697   $138.97   $138.95   $139.00  
  7 purchase totals = $955.77       $1,013.3016   $1,013.31   $1,013.25   $1,013.30