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 $150.91   8.659%   $163.9773   $163.98   $164.00   $164.00  
  Purchase #2 $131.87   13.336%   $149.4562   $149.46   $149.45   $149.50  
  Purchase #3 $98.78   13.171%   $111.7903   $111.79   $111.80   $111.80  
  Purchase #4 $248.53   8.180%   $268.8598   $268.86   $268.85   $268.90  
  Purchase #5 $62.49   8.127%   $67.5686   $67.57   $67.55   $67.60  
  Purchase #6 $71.91   10.702%   $79.6058   $79.61   $79.60   $79.60  
  Purchase #7 $249.99   4.373%   $260.9221   $260.92   $260.90   $260.90  
  7 purchase totals = $1,014.48       $1,102.1801   $1,102.19   $1,102.15   $1,102.30