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 $188.82   8.278%   $204.4505   $204.45   $204.45   $204.50  
  Purchase #2 $49.52   5.444%   $52.2159   $52.22   $52.20   $52.20  
  Purchase #3 $101.52   9.539%   $111.204   $111.20   $111.20   $111.20  
  Purchase #4 $101.89   12.452%   $114.5773   $114.58   $114.60   $114.60  
  Purchase #5 $228.45   5.173%   $240.2677   $240.27   $240.25   $240.30  
  Purchase #6 $243.27   6.871%   $259.9851   $259.99   $260.00   $260.00  
  Purchase #7 $218.91   8.500%   $237.5174   $237.52   $237.50   $237.50  
  7 purchase totals = $1,132.38       $1,220.2179   $1,220.23   $1,220.20   $1,220.30