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 $44.26   6.132%   $46.974   $46.97   $46.95   $47.00  
  Purchase #2 $65.80   4.654%   $68.8623   $68.86   $68.85   $68.90  
  Purchase #3 $182.99   5.451%   $192.9648   $192.96   $192.95   $193.00  
  Purchase #4 $176.96   8.478%   $191.9627   $191.96   $191.95   $192.00  
  Purchase #5 $80.59   5.280%   $84.8452   $84.85   $84.85   $84.80  
  Purchase #6 $171.26   6.110%   $181.724   $181.72   $181.70   $181.70  
  Purchase #7 $29.60   5.510%   $31.231   $31.23   $31.25   $31.20  
  7 purchase totals = $751.46       $798.5640   $798.55   $798.50   $798.60