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 $238.47   12.186%   $267.53   $267.53   $267.55   $267.50  
  Purchase #2 $128.47   4.390%   $134.1098   $134.11   $134.10   $134.10  
  Purchase #3 $156.83   5.494%   $165.4462   $165.45   $165.45   $165.40  
  Purchase #4 $34.88   7.766%   $37.5888   $37.59   $37.60   $37.60  
  Purchase #5 $92.86   4.403%   $96.9486   $96.95   $96.95   $96.90  
  Purchase #6 $197.55   4.613%   $206.663   $206.66   $206.65   $206.70  
  Purchase #7 $131.60   8.806%   $143.1887   $143.19   $143.20   $143.20  
  7 purchase totals = $980.66       $1,051.4751   $1,051.48   $1,051.50   $1,051.40