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 $193.74   5.525%   $204.4441   $204.44   $204.45   $204.40  
  Purchase #2 $126.31   13.217%   $143.0044   $143.00   $143.00   $143.00  
  Purchase #3 $31.99   10.312%   $35.2888   $35.29   $35.30   $35.30  
  Purchase #4 $211.48   5.718%   $223.5724   $223.57   $223.55   $223.60  
  Purchase #5 $162.28   3.872%   $168.5635   $168.56   $168.55   $168.60  
  Purchase #6 $155.44   12.217%   $174.4301   $174.43   $174.45   $174.40  
  Purchase #7 $72.37   6.769%   $77.2687   $77.27   $77.25   $77.30  
  7 purchase totals = $953.61       $1,026.5720   $1,026.56   $1,026.55   $1,026.60