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 $153.80   3.843%   $159.7105   $159.71   $159.70   $159.70  
  Purchase #2 $156.57   13.283%   $177.3672   $177.37   $177.35   $177.40  
  Purchase #3 $58.51   13.686%   $66.5177   $66.52   $66.50   $66.50  
  Purchase #4 $78.93   11.474%   $87.9864   $87.99   $88.00   $88.00  
  Purchase #5 $49.42   12.183%   $55.4408   $55.44   $55.45   $55.40  
  Purchase #6 $200.66   9.784%   $220.2926   $220.29   $220.30   $220.30  
  Purchase #7 $164.82   13.220%   $186.6092   $186.61   $186.60   $186.60  
  7 purchase totals = $862.71       $953.9244   $953.93   $953.90   $953.90