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 $52.96   13.233%   $59.9682   $59.97   $59.95   $60.00  
  Purchase #2 $166.43   9.269%   $181.8564   $181.86   $181.85   $181.90  
  Purchase #3 $201.84   6.353%   $214.6629   $214.66   $214.65   $214.70  
  Purchase #4 $203.46   7.726%   $219.1793   $219.18   $219.20   $219.20  
  Purchase #5 $139.90   12.618%   $157.5526   $157.55   $157.55   $157.60  
  Purchase #6 $23.25   13.217%   $26.323   $26.32   $26.30   $26.30  
  Purchase #7 $219.79   3.141%   $226.6936   $226.69   $226.70   $226.70  
  7 purchase totals = $1,007.63       $1,086.2360   $1,086.23   $1,086.20   $1,086.40