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 $138.62   3.230%   $143.0974   $143.10   $143.10   $143.10  
  Purchase #2 $143.67   7.870%   $154.9768   $154.98   $155.00   $155.00  
  Purchase #3 $194.77   12.504%   $219.124   $219.12   $219.10   $219.10  
  Purchase #4 $43.66   7.645%   $46.9978   $47.00   $47.00   $47.00  
  Purchase #5 $225.89   5.573%   $238.4788   $238.48   $238.50   $238.50  
  Purchase #6 $81.30   12.266%   $91.2723   $91.27   $91.25   $91.30  
  Purchase #7 $243.59   5.671%   $257.404   $257.40   $257.40   $257.40  
  7 purchase totals = $1,071.50       $1,151.3511   $1,151.35   $1,151.35   $1,151.40