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 $65.60   4.500%   $68.552   $68.55   $68.55   $68.60  
  Purchase #2 $236.64   13.783%   $269.2561   $269.26   $269.25   $269.30  
  Purchase #3 $192.74   4.401%   $201.2225   $201.22   $201.20   $201.20  
  Purchase #4 $211.52   4.777%   $221.6243   $221.62   $221.60   $221.60  
  Purchase #5 $216.77   5.608%   $228.9265   $228.93   $228.95   $228.90  
  Purchase #6 $231.58   13.392%   $262.5932   $262.59   $262.60   $262.60  
  Purchase #7 $243.60   5.232%   $256.3452   $256.35   $256.35   $256.30  
  7 purchase totals = $1,398.45       $1,508.5198   $1,508.52   $1,508.50   $1,508.50