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 $145.36   6.768%   $155.198   $155.20   $155.20   $155.20  
  Purchase #2 $201.44   8.702%   $218.9693   $218.97   $218.95   $219.00  
  Purchase #3 $248.32   10.322%   $273.9516   $273.95   $273.95   $274.00  
  Purchase #4 $82.37   12.615%   $92.761   $92.76   $92.75   $92.80  
  Purchase #5 $56.27   5.697%   $59.4757   $59.48   $59.50   $59.50  
  Purchase #6 $232.89   11.647%   $260.0147   $260.01   $260.00   $260.00  
  Purchase #7 $22.94   12.425%   $25.7903   $25.79   $25.80   $25.80  
  7 purchase totals = $989.59       $1,086.1606   $1,086.16   $1,086.15   $1,086.30