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 $67.75   5.661%   $71.5853   $71.59   $71.60   $71.60  
  Purchase #2 $227.95   5.648%   $240.8246   $240.82   $240.80   $240.80  
  Purchase #3 $203.98   5.250%   $214.689   $214.69   $214.70   $214.70  
  Purchase #4 $61.69   6.365%   $65.6166   $65.62   $65.60   $65.60  
  Purchase #5 $176.77   9.723%   $193.9573   $193.96   $193.95   $194.00  
  Purchase #6 $99.25   4.816%   $104.0299   $104.03   $104.05   $104.00  
  Purchase #7 $226.49   5.169%   $238.1973   $238.20   $238.20   $238.20  
  7 purchase totals = $1,063.88       $1,128.9000   $1,128.91   $1,128.90   $1,128.90