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 $246.27   8.721%   $267.7472   $267.75   $267.75   $267.70  
  Purchase #2 $147.88   3.525%   $153.0928   $153.09   $153.10   $153.10  
  Purchase #3 $31.43   8.442%   $34.0833   $34.08   $34.10   $34.10  
  Purchase #4 $42.50   8.713%   $46.203   $46.20   $46.20   $46.20  
  Purchase #5 $136.51   10.195%   $150.4272   $150.43   $150.45   $150.40  
  Purchase #6 $91.25   5.861%   $96.5982   $96.60   $96.60   $96.60  
  Purchase #7 $79.96   10.783%   $88.5821   $88.58   $88.60   $88.60  
  7 purchase totals = $775.80       $836.7338   $836.73   $836.80   $836.70