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 $109.37   10.723%   $121.0977   $121.10   $121.10   $121.10  
  Purchase #2 $49.37   9.568%   $54.0937   $54.09   $54.10   $54.10  
  Purchase #3 $152.63   13.783%   $173.667   $173.67   $173.65   $173.70  
  Purchase #4 $172.64   13.603%   $196.1242   $196.12   $196.10   $196.10  
  Purchase #5 $232.37   6.171%   $246.7096   $246.71   $246.70   $246.70  
  Purchase #6 $52.42   9.415%   $57.3553   $57.36   $57.35   $57.40  
  Purchase #7 $164.96   11.152%   $183.3563   $183.36   $183.35   $183.40  
  7 purchase totals = $933.76       $1,032.4038   $1,032.41   $1,032.35   $1,032.50