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 $61.43   10.790%   $68.0583   $68.06   $68.05   $68.10  
  Purchase #2 $10.30   3.113%   $10.6206   $10.62   $10.60   $10.60  
  Purchase #3 $75.50   12.569%   $84.9896   $84.99   $85.00   $85.00  
  Purchase #4 $175.45   5.404%   $184.9313   $184.93   $184.95   $184.90  
  Purchase #5 $223.46   7.667%   $240.5927   $240.59   $240.60   $240.60  
  Purchase #6 $246.85   10.129%   $271.8534   $271.85   $271.85   $271.90  
  Purchase #7 $149.82   3.154%   $154.5453   $154.55   $154.55   $154.50  
  7 purchase totals = $942.81       $1,015.5912   $1,015.59   $1,015.60   $1,015.60