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 $59.54   5.422%   $62.7683   $62.77   $62.75   $62.80  
  Purchase #2 $244.94   3.158%   $252.6752   $252.68   $252.70   $252.70  
  Purchase #3 $128.64   4.414%   $134.3182   $134.32   $134.30   $134.30  
  Purchase #4 $14.99   13.838%   $17.0643   $17.06   $17.05   $17.10  
  Purchase #5 $33.82   13.864%   $38.5088   $38.51   $38.50   $38.50  
  Purchase #6 $97.82   8.398%   $106.0349   $106.03   $106.05   $106.00  
  Purchase #7 $173.27   13.568%   $196.7793   $196.78   $196.80   $196.80  
  7 purchase totals = $753.02       $808.1490   $808.15   $808.15   $808.20