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 $130.25   13.304%   $147.5785   $147.58   $147.60   $147.60  
  Purchase #2 $228.50   7.209%   $244.9726   $244.97   $244.95   $245.00  
  Purchase #3 $110.53   13.153%   $125.068   $125.07   $125.05   $125.10  
  Purchase #4 $99.87   12.698%   $112.5515   $112.55   $112.55   $112.60  
  Purchase #5 $150.32   8.116%   $162.52   $162.52   $162.50   $162.50  
  Purchase #6 $183.48   11.836%   $205.1967   $205.20   $205.20   $205.20  
  Purchase #7 $57.40   12.122%   $64.358   $64.36   $64.35   $64.40  
  7 purchase totals = $960.35       $1,062.2453   $1,062.25   $1,062.20   $1,062.40