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 $32.69   4.153%   $34.0476   $34.05   $34.05   $34.00  
  Purchase #2 $166.28   8.705%   $180.7547   $180.75   $180.75   $180.80  
  Purchase #3 $246.55   11.827%   $275.7095   $275.71   $275.70   $275.70  
  Purchase #4 $69.94   7.661%   $75.2981   $75.30   $75.30   $75.30  
  Purchase #5 $239.51   11.282%   $266.5315   $266.53   $266.55   $266.50  
  Purchase #6 $204.95   5.785%   $216.8064   $216.81   $216.80   $216.80  
  Purchase #7 $202.52   9.819%   $222.4054   $222.41   $222.40   $222.40  
  7 purchase totals = $1,162.44       $1,271.5532   $1,271.56   $1,271.55   $1,271.50