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 $219.78   6.762%   $234.6415   $234.64   $234.65   $234.60  
  Purchase #2 $181.98   4.195%   $189.6141   $189.61   $189.60   $189.60  
  Purchase #3 $13.57   12.234%   $15.2302   $15.23   $15.25   $15.20  
  Purchase #4 $84.98   12.639%   $95.7206   $95.72   $95.70   $95.70  
  Purchase #5 $176.35   6.201%   $187.2855   $187.29   $187.30   $187.30  
  Purchase #6 $186.31   11.671%   $208.0542   $208.05   $208.05   $208.10  
  Purchase #7 $99.65   6.365%   $105.9927   $105.99   $106.00   $106.00  
  7 purchase totals = $962.62       $1,036.5388   $1,036.53   $1,036.55   $1,036.50