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 $71.40   8.758%   $77.6532   $77.65   $77.65   $77.70  
  Purchase #2 $122.96   8.587%   $133.5186   $133.52   $133.50   $133.50  
  Purchase #3 $159.82   10.511%   $176.6187   $176.62   $176.60   $176.60  
  Purchase #4 $218.29   7.340%   $234.3125   $234.31   $234.30   $234.30  
  Purchase #5 $118.53   6.573%   $126.321   $126.32   $126.30   $126.30  
  Purchase #6 $177.80   12.130%   $199.3671   $199.37   $199.35   $199.40  
  Purchase #7 $96.75   10.112%   $106.5334   $106.53   $106.55   $106.50  
  7 purchase totals = $965.55       $1,054.3245   $1,054.32   $1,054.25   $1,054.30