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 $73.47   12.697%   $82.7985   $82.80   $82.80   $82.80  
  Purchase #2 $196.49   3.498%   $203.3632   $203.36   $203.35   $203.40  
  Purchase #3 $218.77   11.378%   $243.6617   $243.66   $243.65   $243.70  
  Purchase #4 $216.69   13.524%   $245.9952   $246.00   $246.00   $246.00  
  Purchase #5 $29.87   12.824%   $33.7005   $33.70   $33.70   $33.70  
  Purchase #6 $57.82   7.811%   $62.3363   $62.34   $62.35   $62.30  
  Purchase #7 $193.58   6.191%   $205.5645   $205.56   $205.55   $205.60  
  7 purchase totals = $986.69       $1,077.4199   $1,077.42   $1,077.40   $1,077.50