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 $113.37   11.130%   $125.9881   $125.99   $126.00   $126.00  
  Purchase #2 $22.96   8.753%   $24.9697   $24.97   $24.95   $25.00  
  Purchase #3 $186.53   7.283%   $200.115   $200.12   $200.10   $200.10  
  Purchase #4 $80.73   6.415%   $85.9088   $85.91   $85.90   $85.90  
  Purchase #5 $12.49   12.623%   $14.0666   $14.07   $14.05   $14.10  
  Purchase #6 $130.65   10.532%   $144.4101   $144.41   $144.40   $144.40  
  Purchase #7 $185.31   8.711%   $201.4524   $201.45   $201.45   $201.50  
  7 purchase totals = $732.04       $796.9107   $796.92   $796.85   $797.00