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 $203.43   11.852%   $227.5405   $227.54   $227.55   $227.50  
  Purchase #2 $54.52   8.565%   $59.1896   $59.19   $59.20   $59.20  
  Purchase #3 $193.36   6.590%   $206.1024   $206.10   $206.10   $206.10  
  Purchase #4 $183.57   3.150%   $189.3525   $189.35   $189.35   $189.40  
  Purchase #5 $30.52   11.580%   $34.0542   $34.05   $34.05   $34.10  
  Purchase #6 $155.49   4.827%   $162.9955   $163.00   $163.00   $163.00  
  Purchase #7 $71.58   7.328%   $76.8254   $76.83   $76.85   $76.80  
  7 purchase totals = $892.47       $956.0601   $956.06   $956.10   $956.10