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 $32.61   4.564%   $34.0983   $34.10   $34.10   $34.10  
  Purchase #2 $54.29   13.184%   $61.4476   $61.45   $61.45   $61.40  
  Purchase #3 $11.59   4.211%   $12.0781   $12.08   $12.10   $12.10  
  Purchase #4 $23.43   8.219%   $25.3557   $25.36   $25.35   $25.40  
  Purchase #5 $123.50   11.422%   $137.6062   $137.61   $137.60   $137.60  
  Purchase #6 $180.93   7.158%   $193.881   $193.88   $193.90   $193.90  
  Purchase #7 $55.44   9.708%   $60.8221   $60.82   $60.80   $60.80  
  7 purchase totals = $481.79       $525.2890   $525.30   $525.30   $525.30