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 $67.29   9.629%   $73.7694   $73.77   $73.75   $73.80  
  Purchase #2 $204.94   3.767%   $212.6601   $212.66   $212.65   $212.70  
  Purchase #3 $180.39   6.831%   $192.7124   $192.71   $192.70   $192.70  
  Purchase #4 $243.45   5.800%   $257.5701   $257.57   $257.55   $257.60  
  Purchase #5 $73.90   5.651%   $78.0761   $78.08   $78.10   $78.10  
  Purchase #6 $63.44   3.272%   $65.5158   $65.52   $65.50   $65.50  
  Purchase #7 $46.95   9.683%   $51.4962   $51.50   $51.50   $51.50  
  7 purchase totals = $880.36       $931.8001   $931.81   $931.75   $931.90