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 $155.88   13.668%   $177.1857   $177.19   $177.20   $177.20  
  Purchase #2 $76.26   10.603%   $84.3458   $84.35   $84.35   $84.30  
  Purchase #3 $173.27   11.377%   $192.9829   $192.98   $193.00   $193.00  
  Purchase #4 $43.62   11.560%   $48.6625   $48.66   $48.65   $48.70  
  Purchase #5 $8.59   12.587%   $9.6712   $9.67   $9.65   $9.70  
  Purchase #6 $219.27   11.426%   $244.3238   $244.32   $244.30   $244.30  
  Purchase #7 $201.26   8.577%   $218.5221   $218.52   $218.50   $218.50  
  7 purchase totals = $878.15       $975.6940   $975.69   $975.65   $975.70