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 $165.25   8.691%   $179.6119   $179.61   $179.60   $179.60  
  Purchase #2 $250.80   12.295%   $281.6359   $281.64   $281.65   $281.60  
  Purchase #3 $36.83   6.234%   $39.126   $39.13   $39.15   $39.10  
  Purchase #4 $128.70   4.268%   $134.1929   $134.19   $134.20   $134.20  
  Purchase #5 $214.53   12.709%   $241.7946   $241.79   $241.80   $241.80  
  Purchase #6 $207.64   8.604%   $225.5053   $225.51   $225.50   $225.50  
  Purchase #7 $136.98   9.667%   $150.2219   $150.22   $150.20   $150.20  
  7 purchase totals = $1,140.73       $1,252.0885   $1,252.09   $1,252.10   $1,252.00