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 $93.77   3.247%   $96.8147   $96.81   $96.80   $96.80  
  Purchase #2 $128.84   12.800%   $145.3315   $145.33   $145.35   $145.30  
  Purchase #3 $137.80   3.327%   $142.3846   $142.38   $142.40   $142.40  
  Purchase #4 $68.28   4.816%   $71.5684   $71.57   $71.55   $71.60  
  Purchase #5 $240.61   13.519%   $273.1381   $273.14   $273.15   $273.10  
  Purchase #6 $60.37   3.856%   $62.6979   $62.70   $62.70   $62.70  
  Purchase #7 $241.54   10.552%   $267.0273   $267.03   $267.05   $267.00  
  7 purchase totals = $971.21       $1,058.9625   $1,058.96   $1,059.00   $1,058.90