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 $124.79   12.148%   $139.9495   $139.95   $139.95   $139.90  
  Purchase #2 $144.26   6.820%   $154.0985   $154.10   $154.10   $154.10  
  Purchase #3 $240.68   5.115%   $252.9908   $252.99   $253.00   $253.00  
  Purchase #4 $84.34   13.654%   $95.8558   $95.86   $95.85   $95.90  
  Purchase #5 $124.71   12.363%   $140.1279   $140.13   $140.15   $140.10  
  Purchase #6 $41.57   9.708%   $45.6056   $45.61   $45.60   $45.60  
  Purchase #7 $225.25   5.297%   $237.1815   $237.18   $237.20   $237.20  
  7 purchase totals = $985.60       $1,065.8096   $1,065.82   $1,065.85   $1,065.80