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 $53.39   11.601%   $59.5838   $59.58   $59.60   $59.60  
  Purchase #2 $100.77   12.841%   $113.7099   $113.71   $113.70   $113.70  
  Purchase #3 $239.43   12.765%   $269.9932   $269.99   $270.00   $270.00  
  Purchase #4 $210.30   13.295%   $238.2594   $238.26   $238.25   $238.30  
  Purchase #5 $69.72   8.648%   $75.7494   $75.75   $75.75   $75.70  
  Purchase #6 $152.62   13.310%   $172.9337   $172.93   $172.95   $172.90  
  Purchase #7 $121.39   4.212%   $126.5029   $126.50   $126.50   $126.50  
  7 purchase totals = $947.62       $1,056.7323   $1,056.72   $1,056.75   $1,056.70