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 $60.49   12.131%   $67.828   $67.83   $67.85   $67.80  
  Purchase #2 $95.36   8.524%   $103.4885   $103.49   $103.50   $103.50  
  Purchase #3 $145.89   8.437%   $158.1987   $158.20   $158.20   $158.20  
  Purchase #4 $199.25   6.710%   $212.6197   $212.62   $212.60   $212.60  
  Purchase #5 $204.55   5.575%   $215.9537   $215.95   $215.95   $216.00  
  Purchase #6 $200.51   11.565%   $223.699   $223.70   $223.70   $223.70  
  Purchase #7 $154.79   8.352%   $167.7181   $167.72   $167.70   $167.70  
  7 purchase totals = $1,060.84       $1,149.5057   $1,149.51   $1,149.50   $1,149.50