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 $58.92   3.710%   $61.1059   $61.11   $61.10   $61.10  
  Purchase #2 $231.34   11.274%   $257.4213   $257.42   $257.40   $257.40  
  Purchase #3 $248.51   8.661%   $270.0335   $270.03   $270.05   $270.00  
  Purchase #4 $117.39   5.721%   $124.1059   $124.11   $124.10   $124.10  
  Purchase #5 $36.72   11.867%   $41.0776   $41.08   $41.10   $41.10  
  Purchase #6 $211.93   5.671%   $223.9486   $223.95   $223.95   $223.90  
  Purchase #7 $210.61   10.632%   $233.0021   $233.00   $233.00   $233.00  
  7 purchase totals = $1,115.42       $1,210.6949   $1,210.70   $1,210.70   $1,210.60