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 $95.36   11.759%   $106.5734   $106.57   $106.55   $106.60  
  Purchase #2 $220.33   9.620%   $241.5257   $241.53   $241.55   $241.50  
  Purchase #3 $92.67   13.290%   $104.9858   $104.99   $105.00   $105.00  
  Purchase #4 $144.75   11.103%   $160.8216   $160.82   $160.80   $160.80  
  Purchase #5 $222.69   4.459%   $232.6197   $232.62   $232.60   $232.60  
  Purchase #6 $23.80   3.803%   $24.7051   $24.71   $24.70   $24.70  
  Purchase #7 $134.36   8.454%   $145.7188   $145.72   $145.70   $145.70  
  7 purchase totals = $933.96       $1,016.9501   $1,016.96   $1,016.90   $1,016.90