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 $206.64   8.750%   $224.721   $224.72   $224.70   $224.70  
  Purchase #2 $104.46   6.663%   $111.4202   $111.42   $111.40   $111.40  
  Purchase #3 $22.88   7.750%   $24.6532   $24.65   $24.65   $24.70  
  Purchase #4 $152.31   9.712%   $167.1023   $167.10   $167.10   $167.10  
  Purchase #5 $186.80   7.611%   $201.0173   $201.02   $201.00   $201.00  
  Purchase #6 $175.43   6.736%   $187.247   $187.25   $187.25   $187.20  
  Purchase #7 $131.86   8.871%   $143.5573   $143.56   $143.55   $143.60  
  7 purchase totals = $980.38       $1,059.7183   $1,059.72   $1,059.65   $1,059.70