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 $70.41   10.130%   $77.5425   $77.54   $77.55   $77.50  
  Purchase #2 $130.61   3.395%   $135.0442   $135.04   $135.05   $135.00  
  Purchase #3 $121.88   3.343%   $125.9544   $125.95   $125.95   $126.00  
  Purchase #4 $250.43   7.581%   $269.4151   $269.42   $269.40   $269.40  
  Purchase #5 $110.99   11.755%   $124.0369   $124.04   $124.05   $124.00  
  Purchase #6 $131.40   10.632%   $145.3704   $145.37   $145.35   $145.40  
  Purchase #7 $169.79   7.846%   $183.1117   $183.11   $183.10   $183.10  
  7 purchase totals = $985.51       $1,060.4752   $1,060.47   $1,060.45   $1,060.40