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 $53.83   12.577%   $60.6002   $60.60   $60.60   $60.60  
  Purchase #2 $250.54   11.260%   $278.7508   $278.75   $278.75   $278.80  
  Purchase #3 $49.26   6.286%   $52.3565   $52.36   $52.35   $52.40  
  Purchase #4 $198.36   11.434%   $221.0405   $221.04   $221.05   $221.00  
  Purchase #5 $130.92   13.338%   $148.3821   $148.38   $148.40   $148.40  
  Purchase #6 $221.36   7.516%   $237.9974   $238.00   $238.00   $238.00  
  Purchase #7 $222.38   3.415%   $229.9743   $229.97   $229.95   $230.00  
  7 purchase totals = $1,126.65       $1,229.1018   $1,229.10   $1,229.10   $1,229.20