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 $153.46   8.808%   $166.9768   $166.98   $167.00   $167.00  
  Purchase #2 $24.42   3.240%   $25.2112   $25.21   $25.20   $25.20  
  Purchase #3 $53.99   13.785%   $61.4325   $61.43   $61.45   $61.40  
  Purchase #4 $74.30   6.297%   $78.9787   $78.98   $79.00   $79.00  
  Purchase #5 $33.25   13.546%   $37.754   $37.75   $37.75   $37.80  
  Purchase #6 $220.31   8.442%   $238.9086   $238.91   $238.90   $238.90  
  Purchase #7 $9.44   6.290%   $10.0338   $10.03   $10.05   $10.00  
  7 purchase totals = $569.17       $619.2956   $619.29   $619.35   $619.30