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 $171.62   13.346%   $194.5244   $194.52   $194.50   $194.50  
  Purchase #2 $189.56   3.153%   $195.5368   $195.54   $195.55   $195.50  
  Purchase #3 $62.79   6.705%   $67.0001   $67.00   $67.00   $67.00  
  Purchase #4 $183.93   5.614%   $194.2558   $194.26   $194.25   $194.30  
  Purchase #5 $22.49   10.861%   $24.9326   $24.93   $24.95   $24.90  
  Purchase #6 $94.26   12.835%   $106.3583   $106.36   $106.35   $106.40  
  Purchase #7 $71.64   3.713%   $74.3   $74.30   $74.30   $74.30  
  7 purchase totals = $796.29       $856.9080   $856.91   $856.90   $856.90