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 $52.52   8.246%   $56.8508   $56.85   $56.85   $56.90  
  Purchase #2 $236.98   9.657%   $259.8652   $259.87   $259.85   $259.90  
  Purchase #3 $237.32   6.108%   $251.8155   $251.82   $251.80   $251.80  
  Purchase #4 $198.84   7.531%   $213.8146   $213.81   $213.80   $213.80  
  Purchase #5 $126.42   9.482%   $138.4071   $138.41   $138.40   $138.40  
  Purchase #6 $136.31   5.237%   $143.4486   $143.45   $143.45   $143.40  
  Purchase #7 $67.91   7.329%   $72.8871   $72.89   $72.90   $72.90  
  7 purchase totals = $1,056.30       $1,137.0889   $1,137.10   $1,137.05   $1,137.10