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 $183.83   5.564%   $194.0583   $194.06   $194.05   $194.10  
  Purchase #2 $61.41   5.318%   $64.6758   $64.68   $64.70   $64.70  
  Purchase #3 $103.94   11.284%   $115.6686   $115.67   $115.65   $115.70  
  Purchase #4 $152.59   10.255%   $168.2381   $168.24   $168.25   $168.20  
  Purchase #5 $76.66   5.299%   $80.7222   $80.72   $80.70   $80.70  
  Purchase #6 $94.35   12.477%   $106.122   $106.12   $106.10   $106.10  
  Purchase #7 $243.29   12.108%   $272.7476   $272.75   $272.75   $272.70  
  7 purchase totals = $916.07       $1,002.2326   $1,002.24   $1,002.20   $1,002.20