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 $224.89   8.473%   $243.9449   $243.94   $243.95   $243.90  
  Purchase #2 $181.55   11.504%   $202.4355   $202.44   $202.45   $202.40  
  Purchase #3 $130.86   4.201%   $136.3574   $136.36   $136.35   $136.40  
  Purchase #4 $89.25   4.645%   $93.3957   $93.40   $93.40   $93.40  
  Purchase #5 $88.29   9.318%   $96.5169   $96.52   $96.50   $96.50  
  Purchase #6 $204.41   12.226%   $229.4012   $229.40   $229.40   $229.40  
  Purchase #7 $232.45   11.672%   $259.5816   $259.58   $259.60   $259.60  
  7 purchase totals = $1,151.70       $1,261.6332   $1,261.64   $1,261.65   $1,261.60