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 $232.62   13.446%   $263.8981   $263.90   $263.90   $263.90  
  Purchase #2 $73.33   5.126%   $77.0889   $77.09   $77.10   $77.10  
  Purchase #3 $40.33   8.369%   $43.7052   $43.71   $43.70   $43.70  
  Purchase #4 $234.65   7.686%   $252.6852   $252.69   $252.70   $252.70  
  Purchase #5 $107.69   3.189%   $111.1242   $111.12   $111.10   $111.10  
  Purchase #6 $187.82   9.124%   $204.9567   $204.96   $204.95   $205.00  
  Purchase #7 $88.72   6.685%   $94.6509   $94.65   $94.65   $94.70  
  7 purchase totals = $965.16       $1,048.1092   $1,048.12   $1,048.10   $1,048.20