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 $189.27   3.295%   $195.5064   $195.51   $195.50   $195.50  
  Purchase #2 $49.84   5.721%   $52.6913   $52.69   $52.70   $52.70  
  Purchase #3 $231.87   3.721%   $240.4979   $240.50   $240.50   $240.50  
  Purchase #4 $184.74   9.629%   $202.5286   $202.53   $202.55   $202.50  
  Purchase #5 $26.26   5.622%   $27.7363   $27.74   $27.75   $27.70  
  Purchase #6 $235.58   3.332%   $243.4295   $243.43   $243.45   $243.40  
  Purchase #7 $64.50   7.455%   $69.3085   $69.31   $69.30   $69.30  
  7 purchase totals = $982.06       $1,031.6985   $1,031.71   $1,031.75   $1,031.60