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 $56.49   7.133%   $60.5194   $60.52   $60.50   $60.50  
  Purchase #2 $197.69   5.602%   $208.7646   $208.76   $208.75   $208.80  
  Purchase #3 $7.59   5.152%   $7.981   $7.98   $8.00   $8.00  
  Purchase #4 $225.90   9.250%   $246.7958   $246.80   $246.80   $246.80  
  Purchase #5 $19.82   13.775%   $22.5502   $22.55   $22.55   $22.60  
  Purchase #6 $68.66   6.231%   $72.9382   $72.94   $72.95   $72.90  
  Purchase #7 $225.97   6.813%   $241.3653   $241.37   $241.35   $241.40  
  7 purchase totals = $802.12       $860.9145   $860.92   $860.90   $861.00