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 $52.43   9.115%   $57.209   $57.21   $57.20   $57.20  
  Purchase #2 $147.95   11.268%   $164.621   $164.62   $164.60   $164.60  
  Purchase #3 $145.29   6.210%   $154.3125   $154.31   $154.30   $154.30  
  Purchase #4 $153.86   7.862%   $165.9565   $165.96   $165.95   $166.00  
  Purchase #5 $228.36   3.773%   $236.976   $236.98   $237.00   $237.00  
  Purchase #6 $154.43   6.711%   $164.7938   $164.79   $164.80   $164.80  
  Purchase #7 $166.68   12.392%   $187.335   $187.34   $187.35   $187.30  
  7 purchase totals = $1,049.00       $1,131.2038   $1,131.21   $1,131.20   $1,131.20