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 $200.49   12.486%   $225.5232   $225.52   $225.50   $225.50  
  Purchase #2 $53.61   5.871%   $56.7574   $56.76   $56.75   $56.80  
  Purchase #3 $27.98   11.221%   $31.1196   $31.12   $31.10   $31.10  
  Purchase #4 $60.91   3.649%   $63.1326   $63.13   $63.15   $63.10  
  Purchase #5 $119.39   3.287%   $123.3143   $123.31   $123.30   $123.30  
  Purchase #6 $50.26   11.444%   $56.0118   $56.01   $56.00   $56.00  
  Purchase #7 $142.74   3.111%   $147.1806   $147.18   $147.20   $147.20  
  7 purchase totals = $655.38       $703.0395   $703.03   $703.00   $703.00