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 $247.28   5.526%   $260.9447   $260.94   $260.95   $260.90  
  Purchase #2 $31.59   13.223%   $35.7671   $35.77   $35.75   $35.80  
  Purchase #3 $25.46   10.482%   $28.1287   $28.13   $28.15   $28.10  
  Purchase #4 $128.36   7.239%   $137.652   $137.65   $137.65   $137.70  
  Purchase #5 $226.91   5.363%   $239.0792   $239.08   $239.10   $239.10  
  Purchase #6 $231.85   5.557%   $244.7339   $244.73   $244.75   $244.70  
  Purchase #7 $223.58   11.514%   $249.323   $249.32   $249.30   $249.30  
  7 purchase totals = $1,115.03       $1,195.6286   $1,195.62   $1,195.65   $1,195.60