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 $214.48   13.810%   $244.0997   $244.10   $244.10   $244.10  
  Purchase #2 $98.91   7.827%   $106.6517   $106.65   $106.65   $106.70  
  Purchase #3 $50.77   9.518%   $55.6023   $55.60   $55.60   $55.60  
  Purchase #4 $123.77   11.869%   $138.4603   $138.46   $138.45   $138.50  
  Purchase #5 $138.99   12.167%   $155.9009   $155.90   $155.90   $155.90  
  Purchase #6 $245.53   3.265%   $253.5466   $253.55   $253.55   $253.50  
  Purchase #7 $67.72   11.398%   $75.4387   $75.44   $75.45   $75.40  
  7 purchase totals = $940.17       $1,029.7002   $1,029.70   $1,029.70   $1,029.70