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 $147.64   13.721%   $167.8977   $167.90   $167.90   $167.90  
  Purchase #2 $200.26   11.681%   $223.6524   $223.65   $223.65   $223.70  
  Purchase #3 $52.35   9.265%   $57.2002   $57.20   $57.20   $57.20  
  Purchase #4 $106.59   8.652%   $115.8122   $115.81   $115.80   $115.80  
  Purchase #5 $196.47   11.525%   $219.1132   $219.11   $219.10   $219.10  
  Purchase #6 $202.44   12.610%   $227.9677   $227.97   $227.95   $228.00  
  Purchase #7 $9.61   12.339%   $10.7958   $10.80   $10.80   $10.80  
  7 purchase totals = $915.36       $1,022.4392   $1,022.44   $1,022.40   $1,022.50