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 $250.87   10.408%   $276.9805   $276.98   $277.00   $277.00  
  Purchase #2 $163.52   7.232%   $175.3458   $175.35   $175.35   $175.30  
  Purchase #3 $142.47   11.392%   $158.7002   $158.70   $158.70   $158.70  
  Purchase #4 $150.44   4.574%   $157.3211   $157.32   $157.30   $157.30  
  Purchase #5 $43.38   11.458%   $48.3505   $48.35   $48.35   $48.40  
  Purchase #6 $203.42   4.149%   $211.8599   $211.86   $211.85   $211.90  
  Purchase #7 $49.81   9.143%   $54.3641   $54.36   $54.35   $54.40  
  7 purchase totals = $1,003.91       $1,082.9221   $1,082.92   $1,082.90   $1,083.00