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 $88.94   10.627%   $98.3917   $98.39   $98.40   $98.40  
  Purchase #2 $202.90   5.475%   $214.0088   $214.01   $214.00   $214.00  
  Purchase #3 $141.55   7.283%   $151.8591   $151.86   $151.85   $151.90  
  Purchase #4 $224.46   13.640%   $255.0763   $255.08   $255.10   $255.10  
  Purchase #5 $69.95   8.347%   $75.7887   $75.79   $75.80   $75.80  
  Purchase #6 $44.31   9.860%   $48.679   $48.68   $48.70   $48.70  
  Purchase #7 $194.96   13.712%   $221.6929   $221.69   $221.70   $221.70  
  7 purchase totals = $967.07       $1,065.4965   $1,065.50   $1,065.55   $1,065.60