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 $182.45   8.475%   $197.9126   $197.91   $197.90   $197.90  
  Purchase #2 $237.84   10.204%   $262.1092   $262.11   $262.10   $262.10  
  Purchase #3 $64.68   3.568%   $66.9878   $66.99   $67.00   $67.00  
  Purchase #4 $221.39   5.167%   $232.8292   $232.83   $232.85   $232.80  
  Purchase #5 $65.64   3.286%   $67.7969   $67.80   $67.80   $67.80  
  Purchase #6 $204.70   11.188%   $227.6018   $227.60   $227.60   $227.60  
  Purchase #7 $6.72   12.566%   $7.5644   $7.56   $7.55   $7.60  
  7 purchase totals = $983.42       $1,062.8019   $1,062.80   $1,062.80   $1,062.80