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 $53.77   13.586%   $61.0752   $61.08   $61.10   $61.10  
  Purchase #2 $211.45   6.254%   $224.6741   $224.67   $224.65   $224.70  
  Purchase #3 $84.70   13.469%   $96.1082   $96.11   $96.10   $96.10  
  Purchase #4 $249.41   10.280%   $275.0493   $275.05   $275.05   $275.00  
  Purchase #5 $61.29   4.238%   $63.8875   $63.89   $63.90   $63.90  
  Purchase #6 $26.25   9.755%   $28.8107   $28.81   $28.80   $28.80  
  Purchase #7 $147.51   8.653%   $160.274   $160.27   $160.25   $160.30  
  7 purchase totals = $834.38       $909.8790   $909.88   $909.85   $909.90