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 $161.48   9.345%   $176.5703   $176.57   $176.55   $176.60  
  Purchase #2 $231.29   12.392%   $259.9515   $259.95   $259.95   $260.00  
  Purchase #3 $22.42   6.108%   $23.7894   $23.79   $23.80   $23.80  
  Purchase #4 $70.37   4.352%   $73.4325   $73.43   $73.45   $73.40  
  Purchase #5 $145.56   7.286%   $156.1655   $156.17   $156.15   $156.20  
  Purchase #6 $45.74   8.230%   $49.5044   $49.50   $49.50   $49.50  
  Purchase #7 $216.74   12.220%   $243.2256   $243.23   $243.25   $243.20  
  7 purchase totals = $893.60       $982.6392   $982.64   $982.65   $982.70