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 $184.93   4.167%   $192.636   $192.64   $192.65   $192.60  
  Purchase #2 $14.98   12.546%   $16.8594   $16.86   $16.85   $16.90  
  Purchase #3 $179.41   10.448%   $198.1548   $198.15   $198.15   $198.20  
  Purchase #4 $211.58   6.764%   $225.8913   $225.89   $225.90   $225.90  
  Purchase #5 $65.32   13.277%   $73.9925   $73.99   $74.00   $74.00  
  Purchase #6 $236.35   3.754%   $245.2226   $245.22   $245.20   $245.20  
  Purchase #7 $203.41   11.690%   $227.1886   $227.19   $227.20   $227.20  
  7 purchase totals = $1,095.98       $1,179.9452   $1,179.94   $1,179.95   $1,180.00