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 $211.98   11.653%   $236.682   $236.68   $236.70   $236.70  
  Purchase #2 $96.30   7.488%   $103.5109   $103.51   $103.50   $103.50  
  Purchase #3 $127.94   9.157%   $139.6555   $139.66   $139.65   $139.70  
  Purchase #4 $178.53   4.680%   $186.8852   $186.89   $186.90   $186.90  
  Purchase #5 $247.36   10.397%   $273.078   $273.08   $273.10   $273.10  
  Purchase #6 $165.85   9.484%   $181.5792   $181.58   $181.60   $181.60  
  Purchase #7 $79.62   4.649%   $83.3215   $83.32   $83.30   $83.30  
  7 purchase totals = $1,107.58       $1,204.7123   $1,204.72   $1,204.75   $1,204.80