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 $61.65   12.854%   $69.5745   $69.57   $69.55   $69.60  
  Purchase #2 $70.60   9.588%   $77.3691   $77.37   $77.35   $77.40  
  Purchase #3 $185.43   6.721%   $197.8928   $197.89   $197.90   $197.90  
  Purchase #4 $110.46   6.443%   $117.5769   $117.58   $117.60   $117.60  
  Purchase #5 $96.70   13.826%   $110.0697   $110.07   $110.05   $110.10  
  Purchase #6 $202.28   10.369%   $223.2544   $223.25   $223.25   $223.30  
  Purchase #7 $211.90   8.783%   $230.5112   $230.51   $230.50   $230.50  
  7 purchase totals = $939.02       $1,026.2486   $1,026.24   $1,026.20   $1,026.40