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 $115.93   4.453%   $121.0924   $121.09   $121.10   $121.10  
  Purchase #2 $236.31   7.844%   $254.8462   $254.85   $254.85   $254.80  
  Purchase #3 $143.64   12.640%   $161.7961   $161.80   $161.80   $161.80  
  Purchase #4 $89.77   5.574%   $94.7738   $94.77   $94.75   $94.80  
  Purchase #5 $141.72   7.537%   $152.4014   $152.40   $152.40   $152.40  
  Purchase #6 $63.48   6.778%   $67.7827   $67.78   $67.80   $67.80  
  Purchase #7 $218.78   7.251%   $234.6437   $234.64   $234.65   $234.60  
  7 purchase totals = $1,009.63       $1,087.3363   $1,087.33   $1,087.35   $1,087.30