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 $208.69   11.421%   $232.5245   $232.52   $232.50   $232.50  
  Purchase #2 $122.84   12.180%   $137.8019   $137.80   $137.80   $137.80  
  Purchase #3 $103.55   3.414%   $107.0852   $107.09   $107.10   $107.10  
  Purchase #4 $24.69   10.787%   $27.3533   $27.35   $27.35   $27.40  
  Purchase #5 $215.29   10.696%   $238.3174   $238.32   $238.30   $238.30  
  Purchase #6 $224.95   4.421%   $234.895   $234.90   $234.90   $234.90  
  Purchase #7 $241.50   5.475%   $254.7221   $254.72   $254.70   $254.70  
  7 purchase totals = $1,141.51       $1,232.6994   $1,232.70   $1,232.65   $1,232.70