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 $233.62   5.814%   $247.2027   $247.20   $247.20   $247.20  
  Purchase #2 $100.64   10.181%   $110.8862   $110.89   $110.90   $110.90  
  Purchase #3 $229.79   5.166%   $241.661   $241.66   $241.65   $241.70  
  Purchase #4 $144.28   5.153%   $151.7147   $151.71   $151.70   $151.70  
  Purchase #5 $122.99   3.693%   $127.532   $127.53   $127.55   $127.50  
  Purchase #6 $31.31   9.249%   $34.2059   $34.21   $34.20   $34.20  
  Purchase #7 $238.90   6.644%   $254.7725   $254.77   $254.75   $254.80  
  7 purchase totals = $1,101.53       $1,167.9750   $1,167.97   $1,167.95   $1,168.00