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 $206.97   13.823%   $235.5795   $235.58   $235.60   $235.60  
  Purchase #2 $247.51   8.320%   $268.1028   $268.10   $268.10   $268.10  
  Purchase #3 $55.26   11.746%   $61.7508   $61.75   $61.75   $61.80  
  Purchase #4 $191.44   12.162%   $214.7229   $214.72   $214.70   $214.70  
  Purchase #5 $187.28   4.787%   $196.2451   $196.25   $196.25   $196.20  
  Purchase #6 $34.95   11.462%   $38.956   $38.96   $38.95   $39.00  
  Purchase #7 $37.52   5.148%   $39.4515   $39.45   $39.45   $39.50  
  7 purchase totals = $960.93       $1,054.8086   $1,054.81   $1,054.80   $1,054.90