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 $117.27   3.821%   $121.7509   $121.75   $121.75   $121.80  
  Purchase #2 $114.93   11.197%   $127.7987   $127.80   $127.80   $127.80  
  Purchase #3 $67.98   7.377%   $72.9949   $72.99   $73.00   $73.00  
  Purchase #4 $117.46   5.158%   $123.5186   $123.52   $123.50   $123.50  
  Purchase #5 $168.42   5.646%   $177.929   $177.93   $177.95   $177.90  
  Purchase #6 $133.51   7.168%   $143.08   $143.08   $143.10   $143.10  
  Purchase #7 $83.28   5.119%   $87.5431   $87.54   $87.55   $87.50  
  7 purchase totals = $802.85       $854.6152   $854.61   $854.65   $854.60