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 $43.37   5.243%   $45.6439   $45.64   $45.65   $45.60  
  Purchase #2 $88.74   7.381%   $95.2899   $95.29   $95.30   $95.30  
  Purchase #3 $82.46   6.284%   $87.6418   $87.64   $87.65   $87.60  
  Purchase #4 $231.77   6.663%   $247.2128   $247.21   $247.20   $247.20  
  Purchase #5 $215.30   12.743%   $242.7357   $242.74   $242.75   $242.70  
  Purchase #6 $181.73   5.699%   $192.0868   $192.09   $192.10   $192.10  
  Purchase #7 $79.43   3.506%   $82.2148   $82.21   $82.20   $82.20  
  7 purchase totals = $922.80       $992.8257   $992.82   $992.85   $992.70