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 $192.67   8.487%   $209.0219   $209.02   $209.00   $209.00  
  Purchase #2 $157.54   6.708%   $168.1078   $168.11   $168.10   $168.10  
  Purchase #3 $6.98   8.379%   $7.5649   $7.56   $7.55   $7.60  
  Purchase #4 $172.28   5.275%   $181.3678   $181.37   $181.35   $181.40  
  Purchase #5 $39.44   9.640%   $43.242   $43.24   $43.25   $43.20  
  Purchase #6 $242.28   3.319%   $250.3213   $250.32   $250.30   $250.30  
  Purchase #7 $184.70   3.648%   $191.4379   $191.44   $191.45   $191.40  
  7 purchase totals = $995.89       $1,051.0636   $1,051.06   $1,051.00   $1,051.00