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 $86.53   10.556%   $95.6641   $95.66   $95.65   $95.70  
  Purchase #2 $159.88   8.182%   $172.9614   $172.96   $172.95   $173.00  
  Purchase #3 $26.65   4.289%   $27.793   $27.79   $27.80   $27.80  
  Purchase #4 $34.71   12.219%   $38.9512   $38.95   $38.95   $39.00  
  Purchase #5 $106.99   6.200%   $113.6234   $113.62   $113.60   $113.60  
  Purchase #6 $249.26   12.229%   $279.742   $279.74   $279.75   $279.70  
  Purchase #7 $29.90   12.228%   $33.5562   $33.56   $33.55   $33.60  
  7 purchase totals = $693.92       $762.2913   $762.28   $762.25   $762.40