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 $54.99   10.804%   $60.9311   $60.93   $60.95   $60.90  
  Purchase #2 $94.52   8.234%   $102.3028   $102.30   $102.30   $102.30  
  Purchase #3 $206.67   8.643%   $224.5325   $224.53   $224.55   $224.50  
  Purchase #4 $112.26   10.870%   $124.4627   $124.46   $124.45   $124.50  
  Purchase #5 $226.84   8.483%   $246.0828   $246.08   $246.10   $246.10  
  Purchase #6 $61.76   12.556%   $69.5146   $69.51   $69.50   $69.50  
  Purchase #7 $175.83   7.807%   $189.557   $189.56   $189.55   $189.60  
  7 purchase totals = $932.87       $1,017.3835   $1,017.37   $1,017.40   $1,017.40