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 $224.59   8.477%   $243.6285   $243.63   $243.65   $243.60  
  Purchase #2 $195.53   6.261%   $207.7721   $207.77   $207.75   $207.80  
  Purchase #3 $181.96   8.717%   $197.8215   $197.82   $197.80   $197.80  
  Purchase #4 $197.71   13.307%   $224.0193   $224.02   $224.00   $224.00  
  Purchase #5 $173.95   13.102%   $196.7409   $196.74   $196.75   $196.70  
  Purchase #6 $196.50   3.597%   $203.5681   $203.57   $203.55   $203.60  
  Purchase #7 $69.52   4.160%   $72.412   $72.41   $72.40   $72.40  
  7 purchase totals = $1,239.76       $1,345.9624   $1,345.96   $1,345.90   $1,345.90