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 $47.67   6.274%   $50.6608   $50.66   $50.65   $50.70  
  Purchase #2 $193.25   13.427%   $219.1977   $219.20   $219.20   $219.20  
  Purchase #3 $226.76   11.438%   $252.6968   $252.70   $252.70   $252.70  
  Purchase #4 $8.76   5.262%   $9.221   $9.22   $9.20   $9.20  
  Purchase #5 $130.46   10.868%   $144.6384   $144.64   $144.65   $144.60  
  Purchase #6 $235.67   12.414%   $264.9261   $264.93   $264.95   $264.90  
  Purchase #7 $108.90   7.740%   $117.3289   $117.33   $117.35   $117.30  
  7 purchase totals = $951.47       $1,058.6697   $1,058.68   $1,058.70   $1,058.60