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 $24.79   6.514%   $26.4048   $26.40   $26.40   $26.40  
  Purchase #2 $222.96   3.617%   $231.0245   $231.02   $231.00   $231.00  
  Purchase #3 $184.27   8.705%   $200.3107   $200.31   $200.30   $200.30  
  Purchase #4 $80.27   9.412%   $87.825   $87.83   $87.85   $87.80  
  Purchase #5 $69.95   5.666%   $73.9134   $73.91   $73.90   $73.90  
  Purchase #6 $146.29   13.474%   $166.0011   $166.00   $166.00   $166.00  
  Purchase #7 $241.85   6.221%   $256.8955   $256.90   $256.90   $256.90  
  7 purchase totals = $970.38       $1,042.3750   $1,042.37   $1,042.35   $1,042.30