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 $169.85   8.144%   $183.6826   $183.68   $183.70   $183.70  
  Purchase #2 $116.80   11.804%   $130.5871   $130.59   $130.60   $130.60  
  Purchase #3 $52.91   13.355%   $59.9761   $59.98   $60.00   $60.00  
  Purchase #4 $29.86   8.855%   $32.5041   $32.50   $32.50   $32.50  
  Purchase #5 $55.40   10.820%   $61.3943   $61.39   $61.40   $61.40  
  Purchase #6 $233.31   8.521%   $253.1903   $253.19   $253.20   $253.20  
  Purchase #7 $48.44   4.714%   $50.7235   $50.72   $50.70   $50.70  
  7 purchase totals = $706.57       $772.0580   $772.05   $772.10   $772.10