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 $222.79   10.829%   $246.9159   $246.92   $246.90   $246.90  
  Purchase #2 $82.81   6.273%   $88.0047   $88.00   $88.00   $88.00  
  Purchase #3 $22.90   8.633%   $24.877   $24.88   $24.90   $24.90  
  Purchase #4 $191.25   8.399%   $207.3131   $207.31   $207.30   $207.30  
  Purchase #5 $190.97   5.309%   $201.1086   $201.11   $201.10   $201.10  
  Purchase #6 $246.48   4.535%   $257.6579   $257.66   $257.65   $257.70  
  Purchase #7 $30.47   11.315%   $33.9177   $33.92   $33.90   $33.90  
  7 purchase totals = $987.67       $1,059.7949   $1,059.80   $1,059.75   $1,059.80