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 $215.35   4.219%   $224.4356   $224.44   $224.45   $224.40  
  Purchase #2 $95.68   9.327%   $104.6041   $104.60   $104.60   $104.60  
  Purchase #3 $159.72   12.264%   $179.3081   $179.31   $179.30   $179.30  
  Purchase #4 $248.32   6.192%   $263.696   $263.70   $263.70   $263.70  
  Purchase #5 $94.49   8.419%   $102.4451   $102.45   $102.45   $102.40  
  Purchase #6 $240.59   10.842%   $266.6748   $266.67   $266.65   $266.70  
  Purchase #7 $29.42   13.743%   $33.4632   $33.46   $33.45   $33.50  
  7 purchase totals = $1,083.57       $1,174.6269   $1,174.63   $1,174.60   $1,174.60