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 $238.42   6.591%   $254.1343   $254.13   $254.15   $254.10  
  Purchase #2 $189.47   8.326%   $205.2453   $205.25   $205.25   $205.20  
  Purchase #3 $239.29   5.577%   $252.6352   $252.64   $252.65   $252.60  
  Purchase #4 $82.30   13.163%   $93.1331   $93.13   $93.15   $93.10  
  Purchase #5 $51.60   8.157%   $55.809   $55.81   $55.80   $55.80  
  Purchase #6 $200.82   8.510%   $217.9098   $217.91   $217.90   $217.90  
  Purchase #7 $80.93   4.678%   $84.7159   $84.72   $84.70   $84.70  
  7 purchase totals = $1,082.83       $1,163.5826   $1,163.59   $1,163.60   $1,163.40