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 $235.59   8.544%   $255.7188   $255.72   $255.70   $255.70  
  Purchase #2 $45.71   10.186%   $50.366   $50.37   $50.35   $50.40  
  Purchase #3 $121.98   10.546%   $134.844   $134.84   $134.85   $134.80  
  Purchase #4 $211.96   5.313%   $223.2214   $223.22   $223.20   $223.20  
  Purchase #5 $12.97   7.309%   $13.918   $13.92   $13.90   $13.90  
  Purchase #6 $180.44   3.615%   $186.9629   $186.96   $186.95   $187.00  
  Purchase #7 $181.39   10.456%   $200.3561   $200.36   $200.35   $200.40  
  7 purchase totals = $990.04       $1,065.3872   $1,065.39   $1,065.30   $1,065.40