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 $77.39   10.140%   $85.2373   $85.24   $85.25   $85.20  
  Purchase #2 $151.51   9.621%   $166.0868   $166.09   $166.10   $166.10  
  Purchase #3 $219.52   12.177%   $246.251   $246.25   $246.25   $246.30  
  Purchase #4 $101.89   11.736%   $113.8478   $113.85   $113.85   $113.80  
  Purchase #5 $120.99   4.107%   $125.9591   $125.96   $125.95   $126.00  
  Purchase #6 $237.48   8.714%   $258.174   $258.17   $258.15   $258.20  
  Purchase #7 $198.65   4.699%   $207.9846   $207.98   $208.00   $208.00  
  7 purchase totals = $1,107.43       $1,203.5406   $1,203.54   $1,203.55   $1,203.60