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 $51.86   13.788%   $59.0105   $59.01   $59.00   $59.00  
  Purchase #2 $229.86   6.873%   $245.6583   $245.66   $245.65   $245.70  
  Purchase #3 $132.53   4.150%   $138.03   $138.03   $138.05   $138.00  
  Purchase #4 $79.57   8.375%   $86.234   $86.23   $86.25   $86.20  
  Purchase #5 $135.85   6.424%   $144.577   $144.58   $144.60   $144.60  
  Purchase #6 $206.73   4.824%   $216.7027   $216.70   $216.70   $216.70  
  Purchase #7 $238.88   8.201%   $258.4705   $258.47   $258.45   $258.50  
  7 purchase totals = $1,075.28       $1,148.6830   $1,148.68   $1,148.70   $1,148.70