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 $146.25   4.446%   $152.7523   $152.75   $152.75   $152.80  
  Purchase #2 $177.97   6.831%   $190.1271   $190.13   $190.15   $190.10  
  Purchase #3 $23.66   13.635%   $26.886   $26.89   $26.90   $26.90  
  Purchase #4 $209.44   12.569%   $235.7645   $235.76   $235.75   $235.80  
  Purchase #5 $96.80   8.845%   $105.362   $105.36   $105.35   $105.40  
  Purchase #6 $70.79   6.353%   $75.2873   $75.29   $75.30   $75.30  
  Purchase #7 $67.27   11.478%   $74.9913   $74.99   $75.00   $75.00  
  7 purchase totals = $792.18       $861.1705   $861.17   $861.20   $861.30