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 $23.43   11.668%   $26.1638   $26.16   $26.15   $26.20  
  Purchase #2 $156.97   5.147%   $165.0492   $165.05   $165.05   $165.00  
  Purchase #3 $236.44   7.482%   $254.1304   $254.13   $254.15   $254.10  
  Purchase #4 $48.85   10.525%   $53.9915   $53.99   $54.00   $54.00  
  Purchase #5 $194.52   10.427%   $214.8026   $214.80   $214.80   $214.80  
  Purchase #6 $44.55   10.177%   $49.0839   $49.08   $49.10   $49.10  
  Purchase #7 $171.62   12.550%   $193.1583   $193.16   $193.15   $193.20  
  7 purchase totals = $876.38       $956.3797   $956.37   $956.40   $956.40