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 $96.85   3.872%   $100.6   $100.60   $100.60   $100.60  
  Purchase #2 $108.98   9.754%   $119.6099   $119.61   $119.60   $119.60  
  Purchase #3 $45.39   13.534%   $51.5331   $51.53   $51.55   $51.50  
  Purchase #4 $184.36   9.643%   $202.1378   $202.14   $202.15   $202.10  
  Purchase #5 $239.45   5.528%   $252.6868   $252.69   $252.70   $252.70  
  Purchase #6 $74.52   5.503%   $78.6208   $78.62   $78.60   $78.60  
  Purchase #7 $212.79   11.180%   $236.5799   $236.58   $236.60   $236.60  
  7 purchase totals = $962.34       $1,041.7683   $1,041.77   $1,041.80   $1,041.70