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 $59.59   9.310%   $65.1378   $65.14   $65.15   $65.10  
  Purchase #2 $123.67   3.303%   $127.7548   $127.75   $127.75   $127.80  
  Purchase #3 $54.48   8.143%   $58.9163   $58.92   $58.90   $58.90  
  Purchase #4 $176.58   6.351%   $187.7946   $187.79   $187.80   $187.80  
  Purchase #5 $25.43   4.467%   $26.566   $26.57   $26.55   $26.60  
  Purchase #6 $185.85   8.240%   $201.164   $201.16   $201.15   $201.20  
  Purchase #7 $180.67   3.357%   $186.7351   $186.74   $186.75   $186.70  
  7 purchase totals = $806.27       $854.0686   $854.07   $854.05   $854.10