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 $134.41   6.121%   $142.6372   $142.64   $142.65   $142.60  
  Purchase #2 $156.51   6.688%   $166.9774   $166.98   $167.00   $167.00  
  Purchase #3 $250.27   7.225%   $268.352   $268.35   $268.35   $268.40  
  Purchase #4 $49.87   13.129%   $56.4174   $56.42   $56.40   $56.40  
  Purchase #5 $176.96   11.723%   $197.705   $197.71   $197.70   $197.70  
  Purchase #6 $246.45   12.323%   $276.82   $276.82   $276.80   $276.80  
  Purchase #7 $8.78   11.359%   $9.7773   $9.78   $9.80   $9.80  
  7 purchase totals = $1,023.25       $1,118.6863   $1,118.70   $1,118.70   $1,118.70