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 $116.25   8.384%   $125.9964   $126.00   $126.00   $126.00  
  Purchase #2 $65.64   5.616%   $69.3263   $69.33   $69.35   $69.30  
  Purchase #3 $80.78   6.369%   $85.9249   $85.92   $85.90   $85.90  
  Purchase #4 $231.64   8.600%   $251.561   $251.56   $251.55   $251.60  
  Purchase #5 $31.57   6.730%   $33.6947   $33.69   $33.70   $33.70  
  Purchase #6 $57.59   5.207%   $60.5887   $60.59   $60.60   $60.60  
  Purchase #7 $80.79   12.631%   $90.9946   $90.99   $91.00   $91.00  
  7 purchase totals = $664.26       $718.0866   $718.08   $718.10   $718.10