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 $90.95   5.261%   $95.7349   $95.73   $95.75   $95.70  
  Purchase #2 $43.36   10.523%   $47.9228   $47.92   $47.90   $47.90  
  Purchase #3 $12.97   12.651%   $14.6108   $14.61   $14.60   $14.60  
  Purchase #4 $112.70   8.167%   $121.9042   $121.90   $121.90   $121.90  
  Purchase #5 $99.30   3.705%   $102.9791   $102.98   $103.00   $103.00  
  Purchase #6 $34.37   11.734%   $38.403   $38.40   $38.40   $38.40  
  Purchase #7 $111.61   7.797%   $120.3122   $120.31   $120.30   $120.30  
  7 purchase totals = $505.26       $541.8670   $541.85   $541.85   $541.80