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 $230.79   11.362%   $257.0124   $257.01   $257.00   $257.00  
  Purchase #2 $59.68   13.703%   $67.858   $67.86   $67.85   $67.90  
  Purchase #3 $48.67   12.592%   $54.7985   $54.80   $54.80   $54.80  
  Purchase #4 $175.60   3.463%   $181.681   $181.68   $181.70   $181.70  
  Purchase #5 $226.78   11.349%   $252.5173   $252.52   $252.50   $252.50  
  Purchase #6 $8.77   13.466%   $9.951   $9.95   $9.95   $10.00  
  Purchase #7 $172.34   11.496%   $192.1522   $192.15   $192.15   $192.20  
  7 purchase totals = $922.63       $1,015.9704   $1,015.97   $1,015.95   $1,016.10