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 $56.28   12.536%   $63.3353   $63.34   $63.35   $63.30  
  Purchase #2 $201.75   13.222%   $228.4254   $228.43   $228.45   $228.40  
  Purchase #3 $199.74   7.811%   $215.3417   $215.34   $215.35   $215.30  
  Purchase #4 $170.70   6.221%   $181.3192   $181.32   $181.30   $181.30  
  Purchase #5 $102.51   4.373%   $106.9928   $106.99   $107.00   $107.00  
  Purchase #6 $32.28   5.218%   $33.9644   $33.96   $33.95   $34.00  
  Purchase #7 $90.88   5.118%   $95.5312   $95.53   $95.55   $95.50  
  7 purchase totals = $854.14       $924.9100   $924.91   $924.95   $924.80