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 $138.40   6.421%   $147.2867   $147.29   $147.30   $147.30  
  Purchase #2 $60.95   3.671%   $63.1875   $63.19   $63.20   $63.20  
  Purchase #3 $203.32   4.435%   $212.3372   $212.34   $212.35   $212.30  
  Purchase #4 $184.94   4.353%   $192.9904   $192.99   $193.00   $193.00  
  Purchase #5 $247.61   4.414%   $258.5395   $258.54   $258.55   $258.50  
  Purchase #6 $202.95   3.611%   $210.2785   $210.28   $210.30   $210.30  
  Purchase #7 $133.41   6.349%   $141.8802   $141.88   $141.90   $141.90  
  7 purchase totals = $1,171.58       $1,226.5000   $1,226.51   $1,226.60   $1,226.50