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 $62.38   12.229%   $70.0085   $70.01   $70.00   $70.00  
  Purchase #2 $250.28   9.226%   $273.3708   $273.37   $273.35   $273.40  
  Purchase #3 $68.88   5.675%   $72.7889   $72.79   $72.80   $72.80  
  Purchase #4 $157.74   10.796%   $174.7696   $174.77   $174.75   $174.80  
  Purchase #5 $200.76   12.349%   $225.5519   $225.55   $225.55   $225.60  
  Purchase #6 $84.79   13.216%   $95.9958   $96.00   $96.00   $96.00  
  Purchase #7 $198.53   8.351%   $215.1092   $215.11   $215.10   $215.10  
  7 purchase totals = $1,023.36       $1,127.5947   $1,127.60   $1,127.55   $1,127.70