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 $89.90   7.344%   $96.5023   $96.50   $96.50   $96.50  
  Purchase #2 $101.73   13.298%   $115.2581   $115.26   $115.25   $115.30  
  Purchase #3 $71.52   12.486%   $80.45   $80.45   $80.45   $80.50  
  Purchase #4 $232.41   4.580%   $243.0544   $243.05   $243.05   $243.10  
  Purchase #5 $106.79   10.570%   $118.0777   $118.08   $118.10   $118.10  
  Purchase #6 $60.39   8.551%   $65.5539   $65.55   $65.55   $65.60  
  Purchase #7 $203.85   13.487%   $231.3432   $231.34   $231.35   $231.30  
  7 purchase totals = $866.59       $950.2396   $950.23   $950.25   $950.40