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 $246.43   6.721%   $262.9926   $262.99   $263.00   $263.00  
  Purchase #2 $87.98   4.289%   $91.7535   $91.75   $91.75   $91.80  
  Purchase #3 $231.52   8.565%   $251.3497   $251.35   $251.35   $251.30  
  Purchase #4 $215.91   4.317%   $225.2308   $225.23   $225.25   $225.20  
  Purchase #5 $166.81   5.736%   $176.3782   $176.38   $176.40   $176.40  
  Purchase #6 $162.89   11.743%   $182.0182   $182.02   $182.00   $182.00  
  Purchase #7 $235.96   4.544%   $246.682   $246.68   $246.70   $246.70  
  7 purchase totals = $1,347.50       $1,436.4050   $1,436.40   $1,436.45   $1,436.40