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 $218.48   13.229%   $247.3827   $247.38   $247.40   $247.40  
  Purchase #2 $198.53   7.133%   $212.6911   $212.69   $212.70   $212.70  
  Purchase #3 $133.75   7.767%   $144.1384   $144.14   $144.15   $144.10  
  Purchase #4 $41.47   6.392%   $44.1208   $44.12   $44.10   $44.10  
  Purchase #5 $158.91   8.402%   $172.2616   $172.26   $172.25   $172.30  
  Purchase #6 $72.28   13.389%   $81.9576   $81.96   $81.95   $82.00  
  Purchase #7 $103.28   4.145%   $107.561   $107.56   $107.55   $107.60  
  7 purchase totals = $926.70       $1,010.1132   $1,010.11   $1,010.10   $1,010.20