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 $88.92   10.865%   $98.5812   $98.58   $98.60   $98.60  
  Purchase #2 $152.81   9.692%   $167.6203   $167.62   $167.60   $167.60  
  Purchase #3 $141.38   12.870%   $159.5756   $159.58   $159.60   $159.60  
  Purchase #4 $113.80   7.133%   $121.9174   $121.92   $121.90   $121.90  
  Purchase #5 $197.51   5.815%   $208.9952   $209.00   $209.00   $209.00  
  Purchase #6 $120.54   5.803%   $127.5349   $127.53   $127.55   $127.50  
  Purchase #7 $136.68   9.496%   $149.6591   $149.66   $149.65   $149.70  
  7 purchase totals = $951.64       $1,033.8837   $1,033.89   $1,033.90   $1,033.90