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 $218.98   11.377%   $243.8934   $243.89   $243.90   $243.90  
  Purchase #2 $191.33   10.783%   $211.9611   $211.96   $211.95   $212.00  
  Purchase #3 $194.74   9.243%   $212.7398   $212.74   $212.75   $212.70  
  Purchase #4 $173.75   6.102%   $184.3522   $184.35   $184.35   $184.40  
  Purchase #5 $84.91   12.296%   $95.3505   $95.35   $95.35   $95.40  
  Purchase #6 $35.97   4.369%   $37.5415   $37.54   $37.55   $37.50  
  Purchase #7 $11.32   4.418%   $11.8201   $11.82   $11.80   $11.80  
  7 purchase totals = $911.00       $997.6586   $997.65   $997.65   $997.70