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 $198.85   12.381%   $223.4696   $223.47   $223.45   $223.50  
  Purchase #2 $96.39   8.354%   $104.4424   $104.44   $104.45   $104.40  
  Purchase #3 $165.55   11.134%   $183.9823   $183.98   $184.00   $184.00  
  Purchase #4 $17.52   10.295%   $19.3237   $19.32   $19.30   $19.30  
  Purchase #5 $158.39   10.225%   $174.5854   $174.59   $174.60   $174.60  
  Purchase #6 $237.30   4.177%   $247.212   $247.21   $247.20   $247.20  
  Purchase #7 $140.28   3.143%   $144.689   $144.69   $144.70   $144.70  
  7 purchase totals = $1,014.28       $1,097.7044   $1,097.70   $1,097.70   $1,097.70