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 $111.48   13.326%   $126.3358   $126.34   $126.35   $126.30  
  Purchase #2 $203.67   10.445%   $224.9433   $224.94   $224.95   $224.90  
  Purchase #3 $115.70   3.739%   $120.026   $120.03   $120.05   $120.00  
  Purchase #4 $37.52   7.375%   $40.2871   $40.29   $40.30   $40.30  
  Purchase #5 $131.72   10.635%   $145.7284   $145.73   $145.75   $145.70  
  Purchase #6 $225.79   3.280%   $233.1959   $233.20   $233.20   $233.20  
  Purchase #7 $65.94   7.657%   $70.989   $70.99   $71.00   $71.00  
  7 purchase totals = $891.82       $961.5055   $961.52   $961.60   $961.40