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 $29.70   11.136%   $33.0074   $33.01   $33.00   $33.00  
  Purchase #2 $147.39   6.384%   $156.7994   $156.80   $156.80   $156.80  
  Purchase #3 $130.89   8.435%   $141.9306   $141.93   $141.95   $141.90  
  Purchase #4 $244.86   9.308%   $267.6516   $267.65   $267.65   $267.70  
  Purchase #5 $205.52   8.255%   $222.4857   $222.49   $222.50   $222.50  
  Purchase #6 $163.89   5.523%   $172.9416   $172.94   $172.95   $172.90  
  Purchase #7 $14.59   10.807%   $16.1667   $16.17   $16.15   $16.20  
  7 purchase totals = $936.84       $1,010.9830   $1,010.99   $1,011.00   $1,011.00