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 $58.87   7.327%   $63.1834   $63.18   $63.20   $63.20  
  Purchase #2 $88.61   6.765%   $94.6045   $94.60   $94.60   $94.60  
  Purchase #3 $247.86   12.380%   $278.5451   $278.55   $278.55   $278.50  
  Purchase #4 $223.46   6.848%   $238.7625   $238.76   $238.75   $238.80  
  Purchase #5 $121.27   11.513%   $135.2318   $135.23   $135.25   $135.20  
  Purchase #6 $84.96   11.829%   $95.0099   $95.01   $95.00   $95.00  
  Purchase #7 $113.45   3.663%   $117.6057   $117.61   $117.60   $117.60  
  7 purchase totals = $938.48       $1,022.9429   $1,022.94   $1,022.95   $1,022.90