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 $235.56   12.544%   $265.1086   $265.11   $265.10   $265.10  
  Purchase #2 $24.46   8.467%   $26.531   $26.53   $26.55   $26.50  
  Purchase #3 $174.27   11.523%   $194.3511   $194.35   $194.35   $194.40  
  Purchase #4 $126.56   7.128%   $135.5812   $135.58   $135.60   $135.60  
  Purchase #5 $69.96   6.527%   $74.5263   $74.53   $74.55   $74.50  
  Purchase #6 $206.72   6.665%   $220.4979   $220.50   $220.50   $220.50  
  Purchase #7 $85.46   13.456%   $96.9595   $96.96   $96.95   $97.00  
  7 purchase totals = $922.99       $1,013.5556   $1,013.56   $1,013.60   $1,013.60