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 $61.95   12.640%   $69.7805   $69.78   $69.80   $69.80  
  Purchase #2 $234.51   13.540%   $266.2627   $266.26   $266.25   $266.30  
  Purchase #3 $22.62   12.771%   $25.5088   $25.51   $25.50   $25.50  
  Purchase #4 $186.36   5.784%   $197.1391   $197.14   $197.15   $197.10  
  Purchase #5 $64.77   10.479%   $71.5572   $71.56   $71.55   $71.60  
  Purchase #6 $138.74   9.558%   $152.0008   $152.00   $152.00   $152.00  
  Purchase #7 $204.33   12.363%   $229.5913   $229.59   $229.60   $229.60  
  7 purchase totals = $913.28       $1,011.8404   $1,011.84   $1,011.85   $1,011.90