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 $42.36   13.632%   $48.1345   $48.13   $48.15   $48.10  
  Purchase #2 $229.63   6.194%   $243.8533   $243.85   $243.85   $243.90  
  Purchase #3 $7.27   4.673%   $7.6097   $7.61   $7.60   $7.60  
  Purchase #4 $238.76   4.824%   $250.2778   $250.28   $250.30   $250.30  
  Purchase #5 $216.99   8.688%   $235.8421   $235.84   $235.85   $235.80  
  Purchase #6 $37.81   3.277%   $39.049   $39.05   $39.05   $39.00  
  Purchase #7 $216.29   13.866%   $246.2808   $246.28   $246.30   $246.30  
  7 purchase totals = $989.11       $1,071.0472   $1,071.04   $1,071.10   $1,071.00