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 $67.76   3.431%   $70.0848   $70.08   $70.10   $70.10  
  Purchase #2 $40.86   8.456%   $44.3151   $44.32   $44.30   $44.30  
  Purchase #3 $132.60   8.592%   $143.993   $143.99   $144.00   $144.00  
  Purchase #4 $106.88   5.330%   $112.5767   $112.58   $112.60   $112.60  
  Purchase #5 $193.62   5.705%   $204.666   $204.67   $204.65   $204.70  
  Purchase #6 $151.31   7.187%   $162.1846   $162.18   $162.20   $162.20  
  Purchase #7 $186.51   3.757%   $193.5172   $193.52   $193.50   $193.50  
  7 purchase totals = $879.54       $931.3374   $931.34   $931.35   $931.40