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 $94.58   12.363%   $106.2729   $106.27   $106.25   $106.30  
  Purchase #2 $216.93   13.556%   $246.337   $246.34   $246.35   $246.30  
  Purchase #3 $135.49   10.560%   $149.7977   $149.80   $149.80   $149.80  
  Purchase #4 $100.74   4.438%   $105.2108   $105.21   $105.20   $105.20  
  Purchase #5 $224.60   10.807%   $248.8725   $248.87   $248.85   $248.90  
  Purchase #6 $86.69   11.662%   $96.7998   $96.80   $96.80   $96.80  
  Purchase #7 $123.97   5.137%   $130.3383   $130.34   $130.35   $130.30  
  7 purchase totals = $983.00       $1,083.6290   $1,083.63   $1,083.60   $1,083.60