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 $206.89   11.863%   $231.4334   $231.43   $231.45   $231.40  
  Purchase #2 $54.64   13.447%   $61.9874   $61.99   $62.00   $62.00  
  Purchase #3 $226.52   13.389%   $256.8488   $256.85   $256.85   $256.80  
  Purchase #4 $173.64   7.153%   $186.0605   $186.06   $186.05   $186.10  
  Purchase #5 $200.65   3.230%   $207.131   $207.13   $207.15   $207.10  
  Purchase #6 $219.29   8.290%   $237.4691   $237.47   $237.45   $237.50  
  Purchase #7 $138.27   10.219%   $152.3998   $152.40   $152.40   $152.40  
  7 purchase totals = $1,219.90       $1,333.3300   $1,333.33   $1,333.35   $1,333.30