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 $125.95   12.323%   $141.4708   $141.47   $141.45   $141.50  
  Purchase #2 $202.28   9.214%   $220.9181   $220.92   $220.90   $220.90  
  Purchase #3 $31.65   10.273%   $34.9014   $34.90   $34.90   $34.90  
  Purchase #4 $34.86   3.196%   $35.9741   $35.97   $35.95   $36.00  
  Purchase #5 $133.35   12.170%   $149.5787   $149.58   $149.60   $149.60  
  Purchase #6 $200.66   12.841%   $226.4268   $226.43   $226.45   $226.40  
  Purchase #7 $228.31   8.860%   $248.5383   $248.54   $248.55   $248.50  
  7 purchase totals = $957.06       $1,057.8082   $1,057.81   $1,057.80   $1,057.80