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 $241.55   7.758%   $260.2894   $260.29   $260.30   $260.30  
  Purchase #2 $52.91   4.325%   $55.1984   $55.20   $55.20   $55.20  
  Purchase #3 $101.30   8.732%   $110.1455   $110.15   $110.15   $110.10  
  Purchase #4 $89.55   4.735%   $93.7902   $93.79   $93.80   $93.80  
  Purchase #5 $39.76   5.432%   $41.9198   $41.92   $41.90   $41.90  
  Purchase #6 $212.39   5.230%   $223.498   $223.50   $223.50   $223.50  
  Purchase #7 $149.93   9.164%   $163.6696   $163.67   $163.65   $163.70  
  7 purchase totals = $887.39       $948.5109   $948.52   $948.50   $948.50