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 $86.92   7.276%   $93.2443   $93.24   $93.25   $93.20  
  Purchase #2 $150.93   6.473%   $160.6997   $160.70   $160.70   $160.70  
  Purchase #3 $110.82   9.687%   $121.5551   $121.56   $121.55   $121.60  
  Purchase #4 $108.76   4.307%   $113.4443   $113.44   $113.45   $113.40  
  Purchase #5 $37.87   10.241%   $41.7483   $41.75   $41.75   $41.70  
  Purchase #6 $163.98   6.113%   $174.0041   $174.00   $174.00   $174.00  
  Purchase #7 $238.31   7.419%   $255.9902   $255.99   $256.00   $256.00  
  7 purchase totals = $897.59       $960.6860   $960.68   $960.70   $960.60