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 $61.25   12.168%   $68.7029   $68.70   $68.70   $68.70  
  Purchase #2 $236.29   8.807%   $257.1001   $257.10   $257.10   $257.10  
  Purchase #3 $215.70   10.201%   $237.7036   $237.70   $237.70   $237.70  
  Purchase #4 $170.69   12.224%   $191.5551   $191.56   $191.55   $191.60  
  Purchase #5 $139.97   3.707%   $145.1587   $145.16   $145.15   $145.20  
  Purchase #6 $183.89   5.756%   $194.4747   $194.47   $194.45   $194.50  
  Purchase #7 $87.43   12.445%   $98.3107   $98.31   $98.30   $98.30  
  7 purchase totals = $1,095.22       $1,193.0058   $1,193.00   $1,192.95   $1,193.10