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 $106.66   10.129%   $117.4636   $117.46   $117.45   $117.50  
  Purchase #2 $108.62   9.250%   $118.6674   $118.67   $118.65   $118.70  
  Purchase #3 $229.47   8.775%   $249.606   $249.61   $249.60   $249.60  
  Purchase #4 $80.25   8.746%   $87.2687   $87.27   $87.25   $87.30  
  Purchase #5 $56.83   6.489%   $60.5177   $60.52   $60.50   $60.50  
  Purchase #6 $249.29   3.774%   $258.6982   $258.70   $258.70   $258.70  
  Purchase #7 $150.31   11.427%   $167.4859   $167.49   $167.50   $167.50  
  7 purchase totals = $981.43       $1,059.7075   $1,059.72   $1,059.65   $1,059.80