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 $54.35   12.585%   $61.1899   $61.19   $61.20   $61.20  
  Purchase #2 $161.70   11.828%   $180.8259   $180.83   $180.85   $180.80  
  Purchase #3 $241.37   3.745%   $250.4093   $250.41   $250.40   $250.40  
  Purchase #4 $217.45   8.489%   $235.9093   $235.91   $235.90   $235.90  
  Purchase #5 $52.52   9.276%   $57.3918   $57.39   $57.40   $57.40  
  Purchase #6 $243.54   9.374%   $266.3694   $266.37   $266.35   $266.40  
  Purchase #7 $228.41   7.189%   $244.8304   $244.83   $244.85   $244.80  
  7 purchase totals = $1,199.34       $1,296.9260   $1,296.93   $1,296.95   $1,296.90