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 $206.46   9.613%   $226.307   $226.31   $226.30   $226.30  
  Purchase #2 $56.91   7.803%   $61.3507   $61.35   $61.35   $61.40  
  Purchase #3 $126.91   12.514%   $142.7915   $142.79   $142.80   $142.80  
  Purchase #4 $202.33   4.434%   $211.3013   $211.30   $211.30   $211.30  
  Purchase #5 $61.69   10.380%   $68.0934   $68.09   $68.10   $68.10  
  Purchase #6 $57.37   13.672%   $65.2136   $65.21   $65.20   $65.20  
  Purchase #7 $238.98   6.222%   $253.8493   $253.85   $253.85   $253.80  
  7 purchase totals = $950.65       $1,028.9068   $1,028.90   $1,028.90   $1,028.90