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 $183.27   9.808%   $201.2451   $201.25   $201.25   $201.20  
  Purchase #2 $34.45   4.268%   $35.9203   $35.92   $35.90   $35.90  
  Purchase #3 $35.40   12.439%   $39.8034   $39.80   $39.80   $39.80  
  Purchase #4 $110.91   10.534%   $122.5933   $122.59   $122.60   $122.60  
  Purchase #5 $147.49   3.369%   $152.4589   $152.46   $152.45   $152.50  
  Purchase #6 $152.39   4.219%   $158.8193   $158.82   $158.80   $158.80  
  Purchase #7 $129.37   5.380%   $136.3301   $136.33   $136.35   $136.30  
  7 purchase totals = $793.28       $847.1704   $847.17   $847.15   $847.10