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 $43.84   4.373%   $45.7571   $45.76   $45.75   $45.80  
  Purchase #2 $244.42   3.447%   $252.8452   $252.85   $252.85   $252.80  
  Purchase #3 $79.25   4.638%   $82.9256   $82.93   $82.95   $82.90  
  Purchase #4 $76.67   12.692%   $86.401   $86.40   $86.40   $86.40  
  Purchase #5 $247.27   11.485%   $275.669   $275.67   $275.65   $275.70  
  Purchase #6 $230.62   10.588%   $255.038   $255.04   $255.05   $255.00  
  Purchase #7 $120.37   8.711%   $130.8554   $130.86   $130.85   $130.90  
  7 purchase totals = $1,042.44       $1,129.4913   $1,129.51   $1,129.50   $1,129.50