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 $186.25   11.546%   $207.7544   $207.75   $207.75   $207.80  
  Purchase #2 $71.93   9.840%   $79.0079   $79.01   $79.00   $79.00  
  Purchase #3 $45.99   11.495%   $51.2766   $51.28   $51.30   $51.30  
  Purchase #4 $190.46   3.260%   $196.669   $196.67   $196.65   $196.70  
  Purchase #5 $206.49   8.580%   $224.2068   $224.21   $224.20   $224.20  
  Purchase #6 $217.78   5.814%   $230.4417   $230.44   $230.45   $230.40  
  Purchase #7 $60.85   7.331%   $65.3109   $65.31   $65.30   $65.30  
  7 purchase totals = $979.75       $1,054.6673   $1,054.67   $1,054.65   $1,054.70