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 $114.44   10.418%   $126.3624   $126.36   $126.35   $126.40  
  Purchase #2 $65.69   12.511%   $73.9085   $73.91   $73.90   $73.90  
  Purchase #3 $56.59   4.859%   $59.3397   $59.34   $59.35   $59.30  
  Purchase #4 $69.50   9.181%   $75.8808   $75.88   $75.90   $75.90  
  Purchase #5 $187.55   7.705%   $202.0007   $202.00   $202.00   $202.00  
  Purchase #6 $212.93   3.462%   $220.3016   $220.30   $220.30   $220.30  
  Purchase #7 $80.58   4.324%   $84.0643   $84.06   $84.05   $84.10  
  7 purchase totals = $787.28       $841.8580   $841.85   $841.85   $841.90