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 $51.42   4.379%   $53.6717   $53.67   $53.65   $53.70  
  Purchase #2 $156.93   11.726%   $175.3316   $175.33   $175.35   $175.30  
  Purchase #3 $140.65   6.819%   $150.2409   $150.24   $150.25   $150.20  
  Purchase #4 $219.66   6.227%   $233.3382   $233.34   $233.35   $233.30  
  Purchase #5 $232.93   8.393%   $252.4798   $252.48   $252.50   $252.50  
  Purchase #6 $203.33   6.709%   $216.9714   $216.97   $216.95   $217.00  
  Purchase #7 $50.81   10.262%   $56.0241   $56.02   $56.00   $56.00  
  7 purchase totals = $1,055.73       $1,138.0577   $1,138.05   $1,138.05   $1,138.00