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 $108.51   7.458%   $116.6027   $116.60   $116.60   $116.60  
  Purchase #2 $149.43   6.590%   $159.2774   $159.28   $159.30   $159.30  
  Purchase #3 $88.97   6.803%   $95.0226   $95.02   $95.00   $95.00  
  Purchase #4 $102.33   11.424%   $114.0202   $114.02   $114.00   $114.00  
  Purchase #5 $87.89   4.117%   $91.5084   $91.51   $91.50   $91.50  
  Purchase #6 $201.65   11.278%   $224.3921   $224.39   $224.40   $224.40  
  Purchase #7 $230.48   12.102%   $258.3727   $258.37   $258.35   $258.40  
  7 purchase totals = $969.26       $1,059.1961   $1,059.19   $1,059.15   $1,059.20