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 $140.97   9.374%   $154.1845   $154.18   $154.20   $154.20  
  Purchase #2 $202.44   4.583%   $211.7178   $211.72   $211.70   $211.70  
  Purchase #3 $59.95   11.765%   $67.0031   $67.00   $67.00   $67.00  
  Purchase #4 $111.60   3.578%   $115.593   $115.59   $115.60   $115.60  
  Purchase #5 $163.68   9.778%   $179.6846   $179.68   $179.70   $179.70  
  Purchase #6 $205.53   4.485%   $214.748   $214.75   $214.75   $214.70  
  Purchase #7 $26.43   8.507%   $28.6784   $28.68   $28.70   $28.70  
  7 purchase totals = $910.60       $971.6094   $971.60   $971.65   $971.60