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 $209.35   12.736%   $236.0128   $236.01   $236.00   $236.00  
  Purchase #2 $44.64   8.775%   $48.5572   $48.56   $48.55   $48.60  
  Purchase #3 $49.98   10.823%   $55.3893   $55.39   $55.40   $55.40  
  Purchase #4 $240.69   5.297%   $253.4393   $253.44   $253.45   $253.40  
  Purchase #5 $142.76   5.470%   $150.569   $150.57   $150.55   $150.60  
  Purchase #6 $171.99   7.817%   $185.4345   $185.43   $185.45   $185.40  
  Purchase #7 $75.93   12.460%   $85.3909   $85.39   $85.40   $85.40  
  7 purchase totals = $935.34       $1,014.7930   $1,014.79   $1,014.80   $1,014.80