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 $131.95   9.339%   $144.2728   $144.27   $144.25   $144.30  
  Purchase #2 $169.96   11.551%   $189.5921   $189.59   $189.60   $189.60  
  Purchase #3 $41.80   13.105%   $47.2779   $47.28   $47.30   $47.30  
  Purchase #4 $181.96   11.582%   $203.0346   $203.03   $203.05   $203.00  
  Purchase #5 $200.97   11.221%   $223.5208   $223.52   $223.50   $223.50  
  Purchase #6 $126.75   5.728%   $134.0102   $134.01   $134.00   $134.00  
  Purchase #7 $10.34   6.273%   $10.9886   $10.99   $11.00   $11.00  
  7 purchase totals = $863.73       $952.6970   $952.69   $952.70   $952.70