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 $34.95   10.569%   $38.6439   $38.64   $38.65   $38.60  
  Purchase #2 $203.56   6.635%   $217.0662   $217.07   $217.05   $217.10  
  Purchase #3 $119.87   9.717%   $131.5178   $131.52   $131.50   $131.50  
  Purchase #4 $217.31   10.713%   $240.5904   $240.59   $240.60   $240.60  
  Purchase #5 $107.65   7.716%   $115.9563   $115.96   $115.95   $116.00  
  Purchase #6 $181.32   13.613%   $206.0031   $206.00   $206.00   $206.00  
  Purchase #7 $138.70   11.261%   $154.319   $154.32   $154.30   $154.30  
  7 purchase totals = $1,003.36       $1,104.0967   $1,104.10   $1,104.05   $1,104.10