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 $190.90   8.448%   $207.0272   $207.03   $207.05   $207.00  
  Purchase #2 $62.26   8.359%   $67.4643   $67.46   $67.45   $67.50  
  Purchase #3 $180.92   12.572%   $203.6653   $203.67   $203.65   $203.70  
  Purchase #4 $152.55   6.523%   $162.5008   $162.50   $162.50   $162.50  
  Purchase #5 $203.42   6.346%   $216.329   $216.33   $216.35   $216.30  
  Purchase #6 $34.98   13.253%   $39.6159   $39.62   $39.60   $39.60  
  Purchase #7 $109.64   11.798%   $122.5753   $122.58   $122.60   $122.60  
  7 purchase totals = $934.67       $1,019.1778   $1,019.19   $1,019.20   $1,019.20