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 $245.93   10.737%   $272.3355   $272.34   $272.35   $272.30  
  Purchase #2 $50.84   8.529%   $55.1761   $55.18   $55.20   $55.20  
  Purchase #3 $86.28   9.149%   $94.1738   $94.17   $94.15   $94.20  
  Purchase #4 $246.67   9.220%   $269.413   $269.41   $269.40   $269.40  
  Purchase #5 $106.34   4.874%   $111.523   $111.52   $111.50   $111.50  
  Purchase #6 $194.97   6.676%   $207.9862   $207.99   $208.00   $208.00  
  Purchase #7 $148.54   11.114%   $165.0487   $165.05   $165.05   $165.00  
  7 purchase totals = $1,079.57       $1,175.6563   $1,175.66   $1,175.65   $1,175.60