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 $57.78   5.590%   $61.0099   $61.01   $61.00   $61.00  
  Purchase #2 $231.84   5.216%   $243.9328   $243.93   $243.95   $243.90  
  Purchase #3 $93.29   9.451%   $102.1068   $102.11   $102.10   $102.10  
  Purchase #4 $214.89   9.497%   $235.2981   $235.30   $235.30   $235.30  
  Purchase #5 $110.70   12.559%   $124.6028   $124.60   $124.60   $124.60  
  Purchase #6 $170.76   7.717%   $183.9375   $183.94   $183.95   $183.90  
  Purchase #7 $63.37   6.582%   $67.541   $67.54   $67.55   $67.50  
  7 purchase totals = $942.63       $1,018.4289   $1,018.43   $1,018.45   $1,018.30