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 $219.35   12.803%   $247.4334   $247.43   $247.45   $247.40  
  Purchase #2 $191.71   5.344%   $201.955   $201.96   $201.95   $202.00  
  Purchase #3 $66.64   13.262%   $75.4778   $75.48   $75.50   $75.50  
  Purchase #4 $207.89   8.872%   $226.334   $226.33   $226.35   $226.30  
  Purchase #5 $103.70   11.595%   $115.724   $115.72   $115.70   $115.70  
  Purchase #6 $228.31   5.474%   $240.8077   $240.81   $240.80   $240.80  
  Purchase #7 $86.32   12.193%   $96.845   $96.85   $96.85   $96.80  
  7 purchase totals = $1,103.92       $1,204.5769   $1,204.58   $1,204.60   $1,204.50