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 $208.82   12.305%   $234.5153   $234.52   $234.50   $234.50  
  Purchase #2 $107.78   5.766%   $113.9946   $113.99   $114.00   $114.00  
  Purchase #3 $240.36   12.691%   $270.8641   $270.86   $270.85   $270.90  
  Purchase #4 $68.71   6.146%   $72.9329   $72.93   $72.95   $72.90  
  Purchase #5 $113.55   3.506%   $117.5311   $117.53   $117.55   $117.50  
  Purchase #6 $173.90   5.487%   $183.4419   $183.44   $183.45   $183.40  
  Purchase #7 $75.82   6.416%   $80.6846   $80.68   $80.70   $80.70  
  7 purchase totals = $988.94       $1,073.9645   $1,073.95   $1,074.00   $1,073.90