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 $65.29   6.214%   $69.3471   $69.35   $69.35   $69.30  
  Purchase #2 $173.53   5.363%   $182.8364   $182.84   $182.85   $182.80  
  Purchase #3 $155.32   8.173%   $168.0143   $168.01   $168.00   $168.00  
  Purchase #4 $119.96   6.701%   $127.9985   $128.00   $128.00   $128.00  
  Purchase #5 $94.30   12.304%   $105.9027   $105.90   $105.90   $105.90  
  Purchase #6 $82.78   13.115%   $93.6366   $93.64   $93.65   $93.60  
  Purchase #7 $225.57   3.603%   $233.6973   $233.70   $233.70   $233.70  
  7 purchase totals = $916.75       $981.4329   $981.44   $981.45   $981.30