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 $68.49   11.853%   $76.6081   $76.61   $76.60   $76.60  
  Purchase #2 $85.53   4.801%   $89.6363   $89.64   $89.65   $89.60  
  Purchase #3 $211.90   6.692%   $226.0803   $226.08   $226.10   $226.10  
  Purchase #4 $250.42   11.582%   $279.4236   $279.42   $279.40   $279.40  
  Purchase #5 $98.36   7.866%   $106.097   $106.10   $106.10   $106.10  
  Purchase #6 $247.84   3.752%   $257.139   $257.14   $257.15   $257.10  
  Purchase #7 $21.31   3.741%   $22.1072   $22.11   $22.10   $22.10  
  7 purchase totals = $983.85       $1,057.0915   $1,057.10   $1,057.10   $1,057.00