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 $241.89   12.616%   $272.4068   $272.41   $272.40   $272.40  
  Purchase #2 $238.35   3.558%   $246.8305   $246.83   $246.85   $246.80  
  Purchase #3 $5.99   11.279%   $6.6656   $6.67   $6.65   $6.70  
  Purchase #4 $61.56   10.500%   $68.0238   $68.02   $68.00   $68.00  
  Purchase #5 $80.29   5.716%   $84.8794   $84.88   $84.90   $84.90  
  Purchase #6 $217.99   11.714%   $243.5253   $243.53   $243.55   $243.50  
  Purchase #7 $113.39   11.316%   $126.2212   $126.22   $126.20   $126.20  
  7 purchase totals = $959.46       $1,048.5526   $1,048.56   $1,048.55   $1,048.50