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 $244.26   12.813%   $275.557   $275.56   $275.55   $275.60  
  Purchase #2 $43.62   8.127%   $47.165   $47.17   $47.15   $47.20  
  Purchase #3 $197.46   3.493%   $204.3573   $204.36   $204.35   $204.40  
  Purchase #4 $26.52   6.654%   $28.2846   $28.28   $28.30   $28.30  
  Purchase #5 $175.64   10.825%   $194.653   $194.65   $194.65   $194.70  
  Purchase #6 $35.36   5.276%   $37.2256   $37.23   $37.25   $37.20  
  Purchase #7 $192.86   12.402%   $216.7785   $216.78   $216.80   $216.80  
  7 purchase totals = $915.72       $1,004.0210   $1,004.03   $1,004.05   $1,004.20