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 $246.86   8.615%   $268.127   $268.13   $268.15   $268.10  
  Purchase #2 $57.42   7.183%   $61.5445   $61.54   $61.55   $61.50  
  Purchase #3 $49.31   6.793%   $52.6596   $52.66   $52.65   $52.70  
  Purchase #4 $113.74   6.412%   $121.033   $121.03   $121.05   $121.00  
  Purchase #5 $80.80   13.166%   $91.4381   $91.44   $91.45   $91.40  
  Purchase #6 $188.57   6.200%   $200.2613   $200.26   $200.25   $200.30  
  Purchase #7 $87.48   10.166%   $96.3732   $96.37   $96.35   $96.40  
  7 purchase totals = $824.18       $891.4367   $891.43   $891.45   $891.40