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 $66.43   4.718%   $69.5642   $69.56   $69.55   $69.60  
  Purchase #2 $116.51   5.311%   $122.6978   $122.70   $122.70   $122.70  
  Purchase #3 $189.45   9.325%   $207.1162   $207.12   $207.10   $207.10  
  Purchase #4 $235.30   10.850%   $260.8301   $260.83   $260.85   $260.80  
  Purchase #5 $120.40   12.647%   $135.627   $135.63   $135.65   $135.60  
  Purchase #6 $106.98   8.216%   $115.7695   $115.77   $115.75   $115.80  
  Purchase #7 $163.90   4.742%   $171.6721   $171.67   $171.65   $171.70  
  7 purchase totals = $998.97       $1,083.2769   $1,083.28   $1,083.25   $1,083.30