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 $246.63   12.305%   $276.9778   $276.98   $277.00   $277.00  
  Purchase #2 $170.47   12.225%   $191.31   $191.31   $191.30   $191.30  
  Purchase #3 $125.91   13.655%   $143.103   $143.10   $143.10   $143.10  
  Purchase #4 $45.68   8.538%   $49.5802   $49.58   $49.60   $49.60  
  Purchase #5 $203.94   4.294%   $212.6972   $212.70   $212.70   $212.70  
  Purchase #6 $101.80   11.296%   $113.2993   $113.30   $113.30   $113.30  
  Purchase #7 $148.71   13.267%   $168.4394   $168.44   $168.45   $168.40  
  7 purchase totals = $1,043.14       $1,155.4069   $1,155.41   $1,155.45   $1,155.40