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 $55.49   8.126%   $59.9991   $60.00   $60.00   $60.00  
  Purchase #2 $59.82   4.197%   $62.3306   $62.33   $62.35   $62.30  
  Purchase #3 $126.54   6.361%   $134.5892   $134.59   $134.60   $134.60  
  Purchase #4 $236.87   7.563%   $254.7845   $254.78   $254.80   $254.80  
  Purchase #5 $57.62   5.606%   $60.8502   $60.85   $60.85   $60.90  
  Purchase #6 $115.67   6.222%   $122.867   $122.87   $122.85   $122.90  
  Purchase #7 $5.85   12.380%   $6.5742   $6.57   $6.55   $6.60  
  7 purchase totals = $657.86       $701.9948   $701.99   $702.00   $702.10