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 $243.68   10.604%   $269.5198   $269.52   $269.50   $269.50  
  Purchase #2 $225.29   6.277%   $239.4315   $239.43   $239.45   $239.40  
  Purchase #3 $38.56   13.165%   $43.6364   $43.64   $43.65   $43.60  
  Purchase #4 $204.96   3.316%   $211.7565   $211.76   $211.75   $211.80  
  Purchase #5 $5.46   11.325%   $6.0783   $6.08   $6.10   $6.10  
  Purchase #6 $72.42   3.235%   $74.7628   $74.76   $74.75   $74.80  
  Purchase #7 $125.92   12.313%   $141.4245   $141.42   $141.40   $141.40  
  7 purchase totals = $916.29       $986.6098   $986.61   $986.60   $986.60