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 $31.74   7.223%   $34.0326   $34.03   $34.05   $34.00  
  Purchase #2 $75.91   8.414%   $82.2971   $82.30   $82.30   $82.30  
  Purchase #3 $102.55   3.347%   $105.9823   $105.98   $106.00   $106.00  
  Purchase #4 $158.65   4.366%   $165.5767   $165.58   $165.60   $165.60  
  Purchase #5 $135.27   5.693%   $142.9709   $142.97   $142.95   $143.00  
  Purchase #6 $199.36   3.596%   $206.529   $206.53   $206.55   $206.50  
  Purchase #7 $63.28   7.419%   $67.9747   $67.97   $67.95   $68.00  
  7 purchase totals = $766.76       $805.3633   $805.36   $805.40   $805.40