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 $56.31   5.502%   $59.4082   $59.41   $59.40   $59.40  
  Purchase #2 $250.68   6.686%   $267.4405   $267.44   $267.45   $267.40  
  Purchase #3 $234.95   12.109%   $263.4001   $263.40   $263.40   $263.40  
  Purchase #4 $142.51   6.529%   $151.8145   $151.81   $151.80   $151.80  
  Purchase #5 $34.40   3.654%   $35.657   $35.66   $35.65   $35.70  
  Purchase #6 $169.41   6.727%   $180.8062   $180.81   $180.80   $180.80  
  Purchase #7 $226.65   7.221%   $243.0164   $243.02   $243.00   $243.00  
  7 purchase totals = $1,114.91       $1,201.5429   $1,201.55   $1,201.50   $1,201.50