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 $32.83   13.142%   $37.1445   $37.14   $37.15   $37.10  
  Purchase #2 $145.70   6.133%   $154.6358   $154.64   $154.65   $154.60  
  Purchase #3 $152.67   5.537%   $161.1233   $161.12   $161.10   $161.10  
  Purchase #4 $50.75   11.236%   $56.4523   $56.45   $56.45   $56.50  
  Purchase #5 $89.79   4.130%   $93.4983   $93.50   $93.50   $93.50  
  Purchase #6 $226.97   6.497%   $241.7162   $241.72   $241.70   $241.70  
  Purchase #7 $224.64   7.319%   $241.0814   $241.08   $241.10   $241.10  
  7 purchase totals = $923.35       $985.6518   $985.65   $985.65   $985.60