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 $67.35   12.364%   $75.6772   $75.68   $75.70   $75.70  
  Purchase #2 $208.76   11.663%   $233.1077   $233.11   $233.10   $233.10  
  Purchase #3 $179.76   9.402%   $196.661   $196.66   $196.65   $196.70  
  Purchase #4 $6.92   3.656%   $7.173   $7.17   $7.15   $7.20  
  Purchase #5 $203.81   10.160%   $224.5171   $224.52   $224.50   $224.50  
  Purchase #6 $141.45   6.477%   $150.6117   $150.61   $150.60   $150.60  
  Purchase #7 $35.74   8.744%   $38.8651   $38.87   $38.85   $38.90  
  7 purchase totals = $843.79       $926.6128   $926.62   $926.55   $926.70