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 $55.81   13.341%   $63.2556   $63.26   $63.25   $63.30  
  Purchase #2 $184.81   13.599%   $209.9423   $209.94   $209.95   $209.90  
  Purchase #3 $104.59   12.853%   $118.033   $118.03   $118.05   $118.00  
  Purchase #4 $192.50   5.642%   $203.3609   $203.36   $203.35   $203.40  
  Purchase #5 $91.74   11.669%   $102.4451   $102.45   $102.45   $102.40  
  Purchase #6 $41.93   10.432%   $46.3041   $46.30   $46.30   $46.30  
  Purchase #7 $247.58   13.853%   $281.8773   $281.88   $281.90   $281.90  
  7 purchase totals = $918.96       $1,025.2183   $1,025.22   $1,025.25   $1,025.20