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 $244.79   10.788%   $271.1979   $271.20   $271.20   $271.20  
  Purchase #2 $234.96   13.322%   $266.2614   $266.26   $266.25   $266.30  
  Purchase #3 $242.57   13.502%   $275.3218   $275.32   $275.30   $275.30  
  Purchase #4 $181.58   8.259%   $196.5767   $196.58   $196.60   $196.60  
  Purchase #5 $223.52   13.206%   $253.0381   $253.04   $253.05   $253.00  
  Purchase #6 $140.36   8.773%   $152.6738   $152.67   $152.65   $152.70  
  Purchase #7 $65.66   6.284%   $69.7861   $69.79   $69.80   $69.80  
  7 purchase totals = $1,333.44       $1,484.8558   $1,484.86   $1,484.85   $1,484.90