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 $37.95   9.677%   $41.6224   $41.62   $41.60   $41.60  
  Purchase #2 $247.26   6.596%   $263.5693   $263.57   $263.55   $263.60  
  Purchase #3 $172.66   3.655%   $178.9707   $178.97   $178.95   $179.00  
  Purchase #4 $180.39   6.744%   $192.5555   $192.56   $192.55   $192.60  
  Purchase #5 $128.83   9.332%   $140.8524   $140.85   $140.85   $140.90  
  Purchase #6 $165.41   11.648%   $184.677   $184.68   $184.70   $184.70  
  Purchase #7 $230.40   6.695%   $245.8253   $245.83   $245.85   $245.80  
  7 purchase totals = $1,162.90       $1,248.0726   $1,248.08   $1,248.05   $1,248.20