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 $53.46   9.557%   $58.5692   $58.57   $58.55   $58.60  
  Purchase #2 $138.59   13.793%   $157.7057   $157.71   $157.70   $157.70  
  Purchase #3 $116.57   9.419%   $127.5497   $127.55   $127.55   $127.50  
  Purchase #4 $134.58   11.571%   $150.1523   $150.15   $150.15   $150.20  
  Purchase #5 $237.27   7.362%   $254.7378   $254.74   $254.75   $254.70  
  Purchase #6 $24.30   6.852%   $25.965   $25.97   $25.95   $26.00  
  Purchase #7 $234.47   4.675%   $245.4315   $245.43   $245.45   $245.40  
  7 purchase totals = $939.24       $1,020.1112   $1,020.12   $1,020.10   $1,020.10