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 $54.55   13.746%   $62.0484   $62.05   $62.05   $62.00  
  Purchase #2 $59.86   10.184%   $65.9561   $65.96   $65.95   $66.00  
  Purchase #3 $114.35   11.753%   $127.7896   $127.79   $127.80   $127.80  
  Purchase #4 $241.62   4.459%   $252.3938   $252.39   $252.40   $252.40  
  Purchase #5 $203.92   12.136%   $228.6677   $228.67   $228.65   $228.70  
  Purchase #6 $15.55   7.767%   $16.7578   $16.76   $16.75   $16.80  
  Purchase #7 $22.63   6.145%   $24.0206   $24.02   $24.00   $24.00  
  7 purchase totals = $712.48       $777.6340   $777.64   $777.60   $777.70