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 $96.53   8.347%   $104.5874   $104.59   $104.60   $104.60  
  Purchase #2 $208.65   12.669%   $235.0839   $235.08   $235.10   $235.10  
  Purchase #3 $68.81   10.263%   $75.872   $75.87   $75.85   $75.90  
  Purchase #4 $179.25   12.668%   $201.9574   $201.96   $201.95   $202.00  
  Purchase #5 $72.50   9.861%   $79.6492   $79.65   $79.65   $79.60  
  Purchase #6 $73.61   9.222%   $80.3983   $80.40   $80.40   $80.40  
  Purchase #7 $148.38   7.866%   $160.0516   $160.05   $160.05   $160.10  
  7 purchase totals = $847.73       $937.5998   $937.60   $937.60   $937.70