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 $83.54   11.166%   $92.8681   $92.87   $92.85   $92.90  
  Purchase #2 $58.39   4.155%   $60.8161   $60.82   $60.80   $60.80  
  Purchase #3 $241.80   7.748%   $260.5347   $260.53   $260.55   $260.50  
  Purchase #4 $129.68   4.721%   $135.8022   $135.80   $135.80   $135.80  
  Purchase #5 $173.53   5.857%   $183.6937   $183.69   $183.70   $183.70  
  Purchase #6 $224.46   7.662%   $241.6581   $241.66   $241.65   $241.70  
  Purchase #7 $107.65   12.194%   $120.7768   $120.78   $120.80   $120.80  
  7 purchase totals = $1,019.05       $1,096.1497   $1,096.15   $1,096.15   $1,096.20