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 $63.33   8.727%   $68.8568   $68.86   $68.85   $68.90  
  Purchase #2 $225.53   3.561%   $233.5611   $233.56   $233.55   $233.60  
  Purchase #3 $140.57   3.785%   $145.8906   $145.89   $145.90   $145.90  
  Purchase #4 $241.30   9.552%   $264.349   $264.35   $264.35   $264.30  
  Purchase #5 $186.91   8.361%   $202.5375   $202.54   $202.55   $202.50  
  Purchase #6 $127.59   5.477%   $134.5781   $134.58   $134.60   $134.60  
  Purchase #7 $36.49   5.145%   $38.3674   $38.37   $38.35   $38.40  
  7 purchase totals = $1,021.72       $1,088.1405   $1,088.15   $1,088.15   $1,088.20