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 $226.80   7.271%   $243.2906   $243.29   $243.30   $243.30  
  Purchase #2 $153.40   8.769%   $166.8516   $166.85   $166.85   $166.90  
  Purchase #3 $22.49   11.331%   $25.0383   $25.04   $25.05   $25.00  
  Purchase #4 $199.70   12.402%   $224.4668   $224.47   $224.45   $224.50  
  Purchase #5 $202.82   9.798%   $222.6923   $222.69   $222.70   $222.70  
  Purchase #6 $88.25   13.437%   $100.1082   $100.11   $100.10   $100.10  
  Purchase #7 $201.57   11.580%   $224.9118   $224.91   $224.90   $224.90  
  7 purchase totals = $1,095.03       $1,207.3596   $1,207.36   $1,207.35   $1,207.40