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 $200.63   6.670%   $214.012   $214.01   $214.00   $214.00  
  Purchase #2 $171.39   7.819%   $184.791   $184.79   $184.80   $184.80  
  Purchase #3 $74.54   13.651%   $84.7155   $84.72   $84.70   $84.70  
  Purchase #4 $41.41   6.727%   $44.1957   $44.20   $44.20   $44.20  
  Purchase #5 $118.68   3.266%   $122.5561   $122.56   $122.55   $122.60  
  Purchase #6 $194.88   12.819%   $219.8617   $219.86   $219.85   $219.90  
  Purchase #7 $35.55   9.704%   $38.9998   $39.00   $39.00   $39.00  
  7 purchase totals = $837.08       $909.1318   $909.14   $909.10   $909.20