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 $91.25   11.533%   $101.7739   $101.77   $101.75   $101.80  
  Purchase #2 $24.69   5.209%   $25.9761   $25.98   $26.00   $26.00  
  Purchase #3 $187.31   7.527%   $201.4088   $201.41   $201.40   $201.40  
  Purchase #4 $156.97   4.325%   $163.759   $163.76   $163.75   $163.80  
  Purchase #5 $93.97   8.323%   $101.7911   $101.79   $101.80   $101.80  
  Purchase #6 $109.47   5.580%   $115.5784   $115.58   $115.60   $115.60  
  Purchase #7 $111.91   7.254%   $120.028   $120.03   $120.05   $120.00  
  7 purchase totals = $775.57       $830.3153   $830.32   $830.35   $830.40