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 $245.52   3.167%   $253.2956   $253.30   $253.30   $253.30  
  Purchase #2 $71.93   3.368%   $74.3526   $74.35   $74.35   $74.40  
  Purchase #3 $245.67   5.654%   $259.5602   $259.56   $259.55   $259.60  
  Purchase #4 $110.40   6.578%   $117.6621   $117.66   $117.65   $117.70  
  Purchase #5 $101.58   8.759%   $110.4774   $110.48   $110.50   $110.50  
  Purchase #6 $175.91   12.291%   $197.5311   $197.53   $197.55   $197.50  
  Purchase #7 $10.77   9.734%   $11.8184   $11.82   $11.80   $11.80  
  7 purchase totals = $961.78       $1,024.6974   $1,024.70   $1,024.70   $1,024.80