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 $130.84   11.468%   $145.8447   $145.84   $145.85   $145.80  
  Purchase #2 $107.67   5.364%   $113.4454   $113.45   $113.45   $113.40  
  Purchase #3 $65.31   6.579%   $69.6067   $69.61   $69.60   $69.60  
  Purchase #4 $62.34   12.777%   $70.3052   $70.31   $70.30   $70.30  
  Purchase #5 $167.70   11.226%   $186.526   $186.53   $186.55   $186.50  
  Purchase #6 $227.36   6.754%   $242.7159   $242.72   $242.70   $242.70  
  Purchase #7 $199.45   3.622%   $206.6741   $206.67   $206.65   $206.70  
  7 purchase totals = $960.67       $1,035.1180   $1,035.13   $1,035.10   $1,035.00