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 $162.47   13.738%   $184.7901   $184.79   $184.80   $184.80  
  Purchase #2 $145.52   10.537%   $160.8534   $160.85   $160.85   $160.90  
  Purchase #3 $246.80   7.850%   $266.1738   $266.17   $266.15   $266.20  
  Purchase #4 $44.90   9.798%   $49.2993   $49.30   $49.30   $49.30  
  Purchase #5 $210.67   11.844%   $235.6218   $235.62   $235.60   $235.60  
  Purchase #6 $100.91   9.405%   $110.4006   $110.40   $110.40   $110.40  
  Purchase #7 $49.57   5.142%   $52.1189   $52.12   $52.10   $52.10  
  7 purchase totals = $960.84       $1,059.2579   $1,059.25   $1,059.20   $1,059.30