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 $172.58   12.858%   $194.7703   $194.77   $194.75   $194.80  
  Purchase #2 $136.55   10.368%   $150.7075   $150.71   $150.70   $150.70  
  Purchase #3 $236.34   9.277%   $258.2653   $258.27   $258.25   $258.30  
  Purchase #4 $104.49   10.252%   $115.2023   $115.20   $115.20   $115.20  
  Purchase #5 $243.86   12.644%   $274.6937   $274.69   $274.70   $274.70  
  Purchase #6 $96.25   11.107%   $106.9405   $106.94   $106.95   $106.90  
  Purchase #7 $56.65   7.661%   $60.99   $60.99   $61.00   $61.00  
  7 purchase totals = $1,046.72       $1,161.5696   $1,161.57   $1,161.55   $1,161.60