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 $59.53   3.114%   $61.3838   $61.38   $61.40   $61.40  
  Purchase #2 $120.78   5.854%   $127.8505   $127.85   $127.85   $127.90  
  Purchase #3 $68.65   9.277%   $75.0187   $75.02   $75.00   $75.00  
  Purchase #4 $89.84   10.287%   $99.0818   $99.08   $99.10   $99.10  
  Purchase #5 $193.25   6.262%   $205.3513   $205.35   $205.35   $205.40  
  Purchase #6 $222.35   10.860%   $246.4972   $246.50   $246.50   $246.50  
  Purchase #7 $31.74   12.202%   $35.6129   $35.61   $35.60   $35.60  
  7 purchase totals = $786.14       $850.7962   $850.79   $850.80   $850.90