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 $87.58   6.710%   $93.4566   $93.46   $93.45   $93.50  
  Purchase #2 $243.42   13.606%   $276.5397   $276.54   $276.55   $276.50  
  Purchase #3 $168.71   7.835%   $181.9284   $181.93   $181.95   $181.90  
  Purchase #4 $13.69   7.198%   $14.6754   $14.68   $14.70   $14.70  
  Purchase #5 $156.62   12.623%   $176.3901   $176.39   $176.40   $176.40  
  Purchase #6 $137.64   4.121%   $143.3121   $143.31   $143.30   $143.30  
  Purchase #7 $130.30   11.827%   $145.7106   $145.71   $145.70   $145.70  
  7 purchase totals = $937.96       $1,032.0129   $1,032.02   $1,032.05   $1,032.00