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 $59.72   6.699%   $63.7206   $63.72   $63.70   $63.70  
  Purchase #2 $246.73   8.524%   $267.7613   $267.76   $267.75   $267.80  
  Purchase #3 $113.48   7.564%   $122.0636   $122.06   $122.05   $122.10  
  Purchase #4 $28.30   13.475%   $32.1134   $32.11   $32.10   $32.10  
  Purchase #5 $159.30   9.807%   $174.9226   $174.92   $174.90   $174.90  
  Purchase #6 $91.71   8.474%   $99.4815   $99.48   $99.50   $99.50  
  Purchase #7 $20.39   11.731%   $22.782   $22.78   $22.80   $22.80  
  7 purchase totals = $719.63       $782.8450   $782.83   $782.80   $782.90