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 $203.88   11.197%   $226.7084   $226.71   $226.70   $226.70  
  Purchase #2 $160.98   9.424%   $176.1508   $176.15   $176.15   $176.20  
  Purchase #3 $152.86   5.777%   $161.6907   $161.69   $161.70   $161.70  
  Purchase #4 $162.62   11.577%   $181.4465   $181.45   $181.45   $181.40  
  Purchase #5 $90.97   4.780%   $95.3184   $95.32   $95.30   $95.30  
  Purchase #6 $195.68   12.606%   $220.3474   $220.35   $220.35   $220.30  
  Purchase #7 $56.45   12.479%   $63.4944   $63.49   $63.50   $63.50  
  7 purchase totals = $1,023.44       $1,125.1566   $1,125.16   $1,125.15   $1,125.10